Method of absorbing sensible and latent heat with series-connected heat sinks

ABSTRACT

A method of absorbing heat from two or more devices can employ a two-phase cooling apparatus that pumps low-pressure coolant through two or more fluidly-connected and series-connected heat sink modules. A flow of subcooled single-phase liquid coolant can be provided to an inlet of a first heat sink module in thermal communication with a first device. Within the first heat sink module, the flow of subcooled single-phase liquid coolant can absorb a first amount of heat from the first device as sensible heat. The flow of subcooled single-phase liquid coolant can be transported from an outlet of the first heat sink module to an inlet of a second heat sink module. Within the second heat sink module, the flow of subcooled single-phase liquid coolant can absorb a second amount of heat from the second device partially as sensible heat and partially as latent heat and thereby transform to two-phase bubbly flow.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 13/169,355 filed Jun. 27, 2011; U.S. patent application Ser.No. 13/169,377 filed Jun. 27, 2011; U.S. patent application Ser. No.14/604,727 filed Jan. 25, 2015; U.S. patent application Ser. No.14/612,276 filed on Feb. 2, 2015; U.S. patent application Ser. No.14/623,524 filed Feb. 17, 2015; U.S. patent application Ser. No.14/644,211 filed Mar. 11, 2015; U.S. patent application Ser. No.14/663,465 filed on Mar. 20, 2015; U.S. patent application Ser. No.14/677,833 filed Apr. 2, 2015; U.S. patent application Ser. No.14/679,026 filed on Apr. 6, 2015; U.S. patent application Ser. No.14/705,972 filed on May 7, 2015; and U.S. patent application Ser. No.14/721,532 filed on May 26, 2015; and claims the benefit of U.S.Provisional Patent Application No. 62/069,301 filed Oct. 27, 2014; U.S.Provisional Patent Application No. 62/072,421 filed Oct. 29, 2014; andU.S. Provisional Patent Application No. 62/099,200 filed Jan. 1, 2015,each of which is hereby incorporated by reference in its entirety as iffully set forth in this description.

FIELD

This disclosure relates to methods and apparatuses for cooling one ormore heat sources, such as one or more heat sources associated with anelectrical, mechanical, chemical, or electromechanical device orprocess.

BACKGROUND

Modern data centers house thousands of servers, and each servertypically includes two or more heat-generating microprocessors. Eachmicroprocessor can easily produce more than 40 thermal watts per squarecentimeter, and future microprocessors are expected to produce evenhigher heat fluxes as semiconductor technology continues to progress. Itfollows that the total amount of heat generated by all servers in a datacenter is substantial. Unfortunately, removing heat from the data centerusing conventional systems is costly and inefficient. For example,removing heat by air conditioning requires significant capitalexpenditures on large air conditioning units as well as significantongoing operating expenditures to power the air conditioning units. Theunits suffer from poor thermodynamic efficiency, which translates tohigh utility bills for data center operators. To reduce the cost ofoperating data centers, and thereby reduce the cost of cloud storageservices that rely on data centers, there is a strong need to coolservers more efficiently.

According to the U.S. Department of Energy, nearly three percent of allelectricity used in the United States is devoted to powering datacenters and computer facilities. Approximately half of this electricitygoes toward power conditioning and cooling. Increasing the efficiency ofcooling systems for data centers and computer facilities would lead todramatic savings in energy nationwide. More efficient cooling systemsare also needed in transportation systems due to increasing adoption ofhybrid and electric vehicles that rely on complex electrical components,including batteries, inverters, and electric motors, which producesignificant amounts of heat that must be effectively dissipated. Coolingsystems capable of more efficiently cooling these electrical componentswould translate to increased range and utility for these vehicles.

Presently, the majority of computers (e.g. servers and personalcomputers) in residential and commercial settings are cooled usingforced air cooling systems in which room air is forced, by one or morefans, over finned heat sinks mounted on microprocessors, power supplies,or other electronic devices. The heat sinks add mass and cost to thecomputers and place mechanical stress on the electronic components towhich they are mounted. If a computer is subject to vibration, such asvibration caused by a fan mounted in the computer, a heat sink mountedon top of a microprocessor can oscillate in response to the vibrationand can fatigue the electrical connections that attach themicroprocessor to the motherboard of the computer.

Another downside of air cooling systems is that cooling fans commonlyoperate at high speeds and can be quite noisy. When many computers arecollocated, such as in a data center, the collective noise produced bythe computer fans can require service personnel to wear hearingprotection. As air passes over electronic devices in the computers, theair, which is at a lower temperature than the surfaces of the electronicdevices, absorbs heat from the electronic devices, thereby cooling thedevices. These air cooling systems are inherently limited in terms ofperformance and efficiency due to the low specific heat of air, which ismuch lower than the specific heat of water and other coolants. Forexample, dry air at 20° C. and 1 bar, has a specific heat of about 1,007J/(kg-K), whereas water at 20° C. has a specific heat of about 4,181J/(kg-K). Due to air's low specific heat and low density, high flowrates are required to ensure adequate cooling of even relatively smallheat loads.

Electronic components within a typical server chassis can produce athermal load of about 500 watts. The amount of airflow required to coolthe components can be calculated with the following equation:

${{flo}{\overset{.}{w}}_{air}} = \frac{Q}{c_{p} \times r \times \Delta \; T}$

where fl{dot over (o)}w_(air) is air flow rate, Q is heat transferred,c_(p) is the specific heat of air, r is density of the air, and ΔT isthe change in temperature between the air entering the server chassisand air exiting the server chassis. Where the thermal load of the serveris 500 W and the maximum allowable ΔT is about 30 degrees, the serverchassis will require about 53 cubic feet per minute (cfm) of air flow.For an installation of 20 servers, which is common in computer rooms ofsmall businesses and academic institutions, over 1,000 cfm of air flowis required to cool the servers. Achieving adequate cooling capacity inthis scenario requires two air conditioning units sized for a typicalU.S. home and an appropriately sized air handler and ducting to delivercool air to the room. Modern data centers, which can have tens ofthousands of servers, must be equipped with many computer room airconditioning (“CRAC”) units each designed to cool and circulate largeamounts of air. The CRAC units are large and expensive and must beprofessionally installed and often require substantial modifications tothe facility, including installation of structural supports, custom airducting, and electrical wiring. After installation, CRAC units requirefrequent preventative maintenance in an attempt to avoid unplanneddowntime. Simply delivering large amounts of cool air to the data centerwill not ensure adequate cooling of the servers. Special care must betaken to deliver cool air to the servers without the cool air firstmixing with warm air exhausting from the servers. This can requireinstallation of special airflow management products, such a raisedfloors, air curtains, and specially designed server enclosures, toassist with air containment. These products can significantly increasethe build-out cost of a data center per square foot and, inevitably, donot succeed at isolating cold air from warm air. Therefore, to ensurethat sensitive components within the servers do not overheat, most datacenters are forced to increase flow rates of cool air well abovetheoretical values as well as decrease the set point temperature of theroom. The result is greater power consumption by the CRAC units andhigher cooling costs for the data center.

Many electronic devices operate less efficiently as their temperatureincreases. As one example, a typical microprocessor operates lessefficiently as its junction temperature increases. FIG. 64 shows a plotof power consumption in watts versus junction temperature. The bottomcurve shows static power consumption of a microprocessor and the topcurves show total power consumption for switching speeds of 1.6 GHz and2.4 GHz, respectively. Total power consumption includes both staticpower consumption and dynamic power consumption, which varies withswitching frequency. As shown in FIG. 64, as the temperature of themicroprocessor increases, it consumes more power to provide the sameperformance. In air cooling systems, it is common for fully utilizedmicroprocessors to operate at or near their maximum rated temperature,resulting in poor operating efficiency. In the example shown in FIG. 64,the microprocessor uses over 35% more power when operating at 95 degreesC. than when operating at 45 degrees C. To conserve energy, it istherefore desirable to provide a cooling system that will allow themicroprocessor to operate consistently at lower temperatures. Providinga consistently lower operating temperature for the microprocessor canalso extend its useful life and can avoid unnecessary throttling ordowntime of the computer due to an unsafe junction temperature.

Operating speeds of next generation microprocessors will continue toincrease, as will heat fluxes (defined as heat load per unit area)produced by those next generation microprocessors. Conventional aircooling systems will soon be incapable of efficiently and effectivelycooling these next generation microprocessors. To effectively cool nextgeneration microprocessors, it is desirable to provide a cooling systemthat is significantly more effective and efficient than existing aircooling systems and is capable of managing high heat fluxes that will beproduced by next generation microprocessors.

Pumped liquid cooling systems can provide improved thermal performanceover conventional air cooling systems. Pumped liquid cooling systemstypically include the following items connected by tubing: a heat sinkattached to the microprocessor, a liquid-to-air heat exchanger, and apump. A liquid coolant is circulated through the system by the pump. Asthe liquid coolant passes through channels in the heat sink, heat fromthe microprocessor is transferred through the thermally conductive heatsink to the coolant, thereby increasing the temperature of the coolantand transferring heat away from the microprocessor. The heat sink istypically designed to maximize heat transfer by maximizing the surfacearea of the channels through which the liquid passes. For example, theheat sink can be a micro-channel heat sink that utilizes fine finchannels through which the liquid coolant flows. The heated liquidcoolant exiting the heat sink is then circulated through a liquid-to-airheat exchanger to reduce the temperature of the liquid coolant before itis circulated back to the pump for another cycle.

Use of closed liquid cooling systems is beginning to migrate from highperformance computers to personal computers. Unfortunately, existingliquid cooling systems have performance constraints that will preventthem from effectively cooling next generation microprocessors. This isbecause liquid cooling systems rely solely on transferring sensible heatby increasing the temperature of a liquid coolant as it passes through aheat sink. The amount of heat that can be transferred is a function of,among other factors, the thermal conductivity of the fluid and the flowrate of the fluid. Dielectric fluids do not have sufficient thermalconductivities to be used in liquid cooling systems. Instead, water or awater-glycol mixture is commonly used due its significantly higherthermal conductivity. Unfortunately, if a leak develops in a liquidcooling system that uses water, the water will destroy the server andpotentially an entire rack of servers. With the price of a single serverbeing thousands of dollars, many data center operators are simplyunwilling to accept the risk of loss that water-based liquid coolingsystems present.

While more effective than air cooling, transferring heat by sensibleheating requires significant flow rates of liquid coolant, and achievinghigh flow rates often necessitates high fluid pressures. Consequently, aliquid cooling system designed to cool a modern microprocessor canrequire a large pump, or a series of small pumps positioned throughoutthe liquid cooling system, to ensure an adequate liquid coolant pressureand flow rate. Operating large pumps, or a series of small pumps, uses asignificant amount of energy and diminishes the efficiency of the liquidcooling system. Moreover, using a series of small pumps increases theprobability of the liquid cooling system experiencing a mechanicalfailure, which translates to unwanted facility downtime.

Although liquid cooling systems have proven adequate at cooling modernmicroprocessors, they will be unable to adequately cool next generationmicroprocessors while maintaining practical physical dimensions andspecifications. For instance, to cool a next generation microprocessor,liquid cooling systems will require very high flow rates (e.g. ofwater), which will require large, heavy duty cooling lines (e.g. greaterthan ¾″ outer diameter), such as rigid copper tubing or reinforcedrubber cooling lines, that will be difficult to route in any practicalmanner into and out of a server housing. If installed in a server, theselarge plumbing lines will block access to electrical components withinthe server, thereby frustrating maintenance of the server. These largeplumbing lines will also prevent drawers on a server rack from openingand closing as intended, thereby preventing the server from being easilyaccessed and further frustrating maintenance of the server. As mentionedabove, water poses a catastrophic risk to servers, and increasing thepressure and flow rates of water into and out of servers only increasesthis risk. Consequently, increasing the capabilities of existing liquidcooling systems to meet the cooling requirements of next generationmicroprocessors is simply not a practical or viable option. Withoutfurther innovation in the area of cooling systems, the implementation ofnext-generation microprocessors will be hampered.

As noted above, liquid cooling systems commonly rely on flowing liquidwater through channels in finned heat sinks. The heat sinks are oftenindirectly coupled to a heat source via a metal base plate that ismounted on the heat source using thermal paste, such as solder thermalinterface material (STIM) or polymer thermal interface material (PTIM),and/or a direct bond adhesive. While this approach can be more effectivethan air cooling, the intervening materials between the water and theheat source induce significant thermal resistance, which reduces theoverall efficiency of the cooling system. The intervening materials alsoadd cost and time to manufacturing and installation processes,constitute additional points of failure, and create potential disposalissues. Finally, the intervening materials render the system unable toadapt to local hot spots on a heat source. Consequently, the liquidcooling system must be designed to accommodate the maximum anticipatedheat load of one or more localized hot spots on the surface of the heatsource (e.g. to adequately cool one hot core of a multicore processor),resulting in additional cost and complexity of the entire liquid coolingsystem.

Unlike water, dielectric coolants can be placed in direct contact withelectronic devices and not harm them. Unfortunately, some dielectriccoolants have a lower specific heat than water, so they are not wellsuited for use in single-phase pumped liquid cooling systems. Forinstance, some dielectric coolants, such as certain hydrofluoroethershave a specific heat of about 1,300 J/(kg-K), whereas water has aspecific heat of about 4,181 J/(kg-K). This means that that cooling amicroprocessor by sensibly warming a flow of dielectric coolant willrequire a flow rate about four times higher than a flow rate of waterused to cool a similar microprocessor by sensibly warming the flow ofwater. This higher flow rate requires more pump power, which translatesto lower cooling system efficiency.

As an alternative to pumped liquid systems, dielectric coolants can beused in immersion cooling systems. Immersion cooling is an aggressiveform of liquid cooling where an entire electronic device (e.g. a server)is submerged in a vat of dielectric coolant (e.g. HFE-7000 or mineraloil). Unfortunately, immersion cooling vats are large, costly, andheavy, especially when filled with dielectric coolant, which can have adensity significantly higher than water. Existing vats hold upwards of250 gallons of coolant and can weigh more than 8,000 pounds when filledwith coolant. Typically, a room must be specially engineered toaccommodate the immersion cooling vat, and containment systems need tobe specially designed and installed in the room as a precaution againstvat failure. When using 250 gallons of coolant, the cost of the coolantbecomes a significant capital expenditure. Certain coolants, such asmineral oil, can act as solvents and, over time, can remove certainidentifying information from motherboards and from other servercomponents. For example, product labels (e.g. stickers containing serialnumbers and bar codes) and other markings (e.g. screen printed valuesand model numbers on capacitors and other devices) are prone to dissolveand wash off due to a continuous flow of the coolant over all surfacesof the server. As the labels and dyes wash off the servers, the coolantin the vat can become contaminated and may need to be replaced,resulting in an additional expense and downtime. Another downside ofimmersion cooling is that servers cannot be serviced immediately afterbeing withdrawn from the vat. Typically, the server must be removed fromthe vat and permitted to drip dry for a period of time (e.g. 24 hours)before a professional can service the server. During this drying period,the server is exposed to contaminants in the air, and the presence ofmineral oil on the server may attract and trap contaminants on sensitivecircuitry of the server, which is not desirable.

Another cooling approach, known as spray cooling or spray evaporativecooling, relies on atomized sprays. In this approach, atomized liquidcoolant is sprayed directly on a surface through air or vapor. As aresult, small droplets impinge on the heated surface forming a thin filmof liquid directly on a heated surface. Heat is then transferred fromthe heated surface to the liquid either by sensible heating of the bulkliquid or by boiling off of a fraction of the liquid through latentheating. This is a very efficient method of removing high heat fluxesfrom small surfaces. Unfortunately, the margin for error in spraycooling systems is very narrow and the onset of dry out and criticalheat flux is a constant concern that can have catastrophic consequences.Critical heat flux is a condition where evaporation of coolant from thesurface to be cooled prevents atomized liquid from reaching and coolingthe surface, often resulting in run-away device temperatures and rapidfailure. Great care must be taken to ensure uniform coverage of thespray on the heated surface and adequate drainage of fluid from theheated surface. Although achievable in static laboratory settings,mainstream adoption of spray cooling has been hampered by severalfactors. First, spray cooling requires a significant working volume toenable atomized sprays to form, which results in non-compact coolingcomponents, making it impractical for packaging in most consumerproducts. Second, atomizing the liquid requires a significant amount ofpressure upstream of the atomizer to generate an appropriate pressuredrop at the atomizer-air interface to enable atomized sprays to form.Maintaining this amount of pressure within the system consumes asignificant amount of energy. Third, high flow rates of atomized spraysare required to prevent dry out or critical heat flux from occurring. Inthe end, it has proven difficult to design a practical and compact spraycooling system, despite a large amount of time and effort that has beenexpended to do so.

In view of the foregoing discussion, efficient, scalable,high-performing methods and apparatuses are needed for cooling devices,such as microprocessors and power electronics that produce high heatfluxes.

SUMMARY

This disclosure relates to methods and apparatuses for cooling one ormore heat sources, such as one or more heat sources in a server,personal computer, high-performance computing system, communicationssystem, vehicle, building, network switch, or other object or electronicdevice. In some examples, a two-phase cooling system having two or moreseries-connected heat sink modules positioned on processors in anelectronic device can maintain the processors at nearly uniformtemperatures by pumping coolant through the series-connected heat sinkmodules and absorbing heat from the processors as sensible heat andlatent heat in the coolant.

In one example, a method of cooling two or more processors of a servercan involve absorbing sensible heat and latent heat in coolant flowingthrough two or more series-connected heat sink modules. The method caninclude providing a flow of subcooled single-phase liquid coolant to aninlet of a first heat sink module in thermal communication with a firstprocessor of a server. The subcooled single-phase liquid coolant canabsorb a first amount of heat from the first processor as sensible heat.The method can include transporting the flow of subcooled single-phaseliquid coolant from an outlet of the first heat sink module to an inletof a second heat sink module in thermal communication with a secondprocessor of the server. The subcooled single-phase liquid can absorb asecond amount of heat from the second processor as sensible heatresulting in the subcooled single-phase liquid coolant reaching itssaturation temperature and becoming saturated single-phase liquidcoolant. The saturated single-phase liquid coolant can absorb a thirdamount of heat from the second processor as latent heat resulting invaporization of a first portion of the saturated single-phase liquidcoolant thereby changing the flow of saturated single-phase liquidcoolant to two-phase bubbly flow including saturated liquid coolant withvapor coolant dispersed as bubbles in the saturated liquid coolant.

The method can include transporting the flow of two-phase bubbly flowcontaining the first amount of heat, the second amount of heat, and thethird amount of heat out of the server through a flexible cooling line.The method can include rejecting the first amount of heat, the secondamount of heat, and the third amount of heat from the flow of two-phasebubbly flow by directing the flow of two-phase bubbly flow through aheat exchanger fluidly connected to a heat rejection loop. The heatrejection loop can then reject the first, second, and third amounts ofheat to a chilled water supply or to ambient air outside of a datacenter facility where the server is located.

The method can include projecting the flow of subcooled single-phaseliquid coolant, in the form of impinging jet streams, against a firstsurface to be cooled within the first heat sink module. Similarly, themethod can include projecting the flow of subcooled single-phase liquidcoolant, in the form of impinging jet streams, against a second surfaceto be cooled within the second heat sink module.

Providing the flow of subcooled single-phase liquid coolant to the inletof the first heat sink module can include providing a flow rate of about0.1-10, 0.2-5, 0.3-2.5, 0.6-1.2, or 0.8-1.1 liters per minute ofsubcooled single-phase liquid coolant to the first inlet of the firstheat sink module. Providing the flow of subcooled single-phase liquidcoolant to the inlet of the first heat sink module can include providinga subcooled single-phase liquid coolant with a boiling point of about15-35, 20-45, 30-55, or 40-65 degrees C. determined at a pressure of 1atm. Providing the flow of subcooled single-phase liquid coolant to theinlet of the first heat sink module can include providing a dielectriccoolant including a hydrofluoroether, a hydrofluorocarbon, or acombination thereof. Providing the flow of subcooled single-phase liquidcoolant to the first heat sink module can include providing a flow ofsubcooled single-phase liquid coolant at a predetermined temperature anda predetermined pressure. The predetermined temperature can be below thesaturation temperature of the flow of subcooled single-phase liquidcoolant at the predetermined pressure. The predetermined temperature canbe about 0.5-20, 0.5-15, 0.5-10, 0.5-7, 0.5-5, 0.5-3, 0.5-1, 1-20, 1-15,1-10, 1-7, 1-5, 1-3, 3-20, 3-15, 3-10, 3-7, 3-5, 5-20, 5-15, 5-10, 5-7,7-20, 7-15, 7-10, 10-20, 10-15, or 15-20 degrees C. below the saturationtemperature of the flow of subcooled single-phase liquid coolant at thepredetermined pressure. The method can include providing a pressuredifferential of about 0.5-5.0, 0.5-3, or 1-3 psi between the inlet ofthe first heat sink module and the outlet of the first heat sink module.The pressure differential can be suitable to promote the flow of coolantto advance from the inlet of the first heat sink module to the outlet ofthe first heat sink module.

The method can include transporting the two-phase bubbly flow having afirst quality from an outlet of the second heat sink module to an inletof a third heat sink module connected in series with the first andsecond heat sink modules. The third heat sink module can be in thermalcommunication with a third processor of the server. The two-phase bubblyflow having the first quality can absorb a fourth amount of heat fromthe third processor as latent heat resulting in vaporization of a secondportion of the saturated single-phase liquid coolant thereby changingthe flow from two-phase bubbly flow with the first quality to two-phasebubbly flow with a second quality greater than the first quality.

The method can include directing the flow of subcooled single-phaseliquid coolant through one or more series-connected heat sink modulesprior to providing the flow of subcooled single-phase liquid coolant tothe inlet of the first heat sink module.

In another example, a method of absorbing heat from two or moreprocessors in an electronic device can involve flowing coolant throughtwo or more fluidly connected heat sink modules arranged in a seriesconfiguration. The method can include providing a flow of subcooledsingle-phase liquid coolant to a first heat sink module. The first heatsink module can include a first thermally conductive base member inthermal communication with a first processor in an electronic device.The subcooled single-phase liquid coolant can have a predeterminedpressure and a predetermined temperature at a first inlet of the firstheat sink module. The predetermined temperature can be below asaturation temperature of the subcooled single-phase liquid coolant atthe predetermined pressure. The method can include projecting the flowof subcooled single-phase liquid coolant against the thermallyconductive base member within the first heat sink module. The subcooledsingle-phase liquid coolant can absorb a first amount of heat from thefirst processor through the thermally conductive base member as sensibleheat. Despite absorbing the first amount of heat, the flow can remainsubcooled single-phase liquid coolant at a temperature below thecoolant's saturation temperature. The method can include providing asecond heat sink module including a second thermally conductive basemember in thermal communication with a second processor. The second heatsink module can include a second inlet. The method can include providinga first section of tubing having a first end connected to the firstoutlet of the first heat sink module and a second end connected to thesecond inlet of the second heat sink module. The method can includetransporting through the first section of tubing the flow of subcooledsingle-phase liquid coolant from the first outlet of the first heat sinkmodule to the second inlet of the second heat sink module. The methodcan include projecting the flow of subcooled single-phase liquid coolantagainst the second thermally conductive base member within the secondheat sink module. The subcooled single-phase liquid coolant can absorb asecond amount of heat from the second processor through the secondthermally conductive base member as sensible heat resulting in thesubcooled single-phase liquid coolant reaching its saturationtemperature and becoming saturated single-phase liquid coolant. Thesaturated single-phase liquid coolant can absorb a third amount of heatfrom the second processor through the second thermally conductive basemember as latent heat resulting in vaporization of a first portion ofthe saturated single-phase liquid coolant thereby changing the flow ofsaturated single-phase liquid coolant to two-phase bubbly flow includingsaturated liquid coolant with vapor coolant dispersed as bubbles in thesaturated liquid coolant.

The method can include directing the flow of subcooled single-phaseliquid coolant through one or more series-connected heat sink modulesprior to providing the flow of subcooled single-phase liquid coolant tothe inlet of the first heat sink module. The method can includetransporting the flow of two-phase bubbly flow containing the firstamount of heat, the second amount of heat, and the third amount of heatout of the electronic device through a flexible cooling line where itcan be rejected to a heat rejection loop. Providing a first section oftubing can include providing a section of flexible tubing having aminimum bend radius of less than 3, 2.5, or 2 inches to permit routingwithin the electronic device. Likewise, providing a flexible coolingline can include providing a flexible cooling line having a minimum bendradius of less than 3, 2.5, or 2 inches to permit routing within theelectronic device.

The electronic device can be a server, a personal computer, a tabletcomputer, a power electronics device, a smartphone, an automotiveelectronic control unit, a battery management device, a progressivegaming device, a telecommunications system, a high performance computingsystem, a server-based gaming device, an avionics system, or a homeautomation control unit. The first processor can be a central processingunit (CPU) or a graphics processing unit (GPU). Likewise, the secondprocessor can be a CPU or GPU.

In yet another example, a method of absorbing heat from two or moredevices can involve using a two-phase cooling apparatus configured topump low-pressure coolant through two or more fluidly-connected andseries-connected heat sink modules. The method can include providing aflow of subcooled single-phase liquid coolant to an inlet of a firstheat sink module in thermal communication with a first device. The flowof subcooled single-phase liquid coolant can absorb a first amount ofheat from the first device as sensible heat within the first heat sinkmodule. The method can include transporting the flow of subcooledsingle-phase liquid coolant from an outlet of the first heat sink moduleto an inlet of a second heat sink module. The flow of subcooledsingle-phase liquid coolant can absorb a second amount of heat from thesecond device partially as sensible heat and partially as latent heatwithin the second heat sink module. As a result, the flow of subcooledsingle-phase liquid coolant can become two-phase bubbly flow includingsaturated liquid coolant with vapor bubbles of coolant dispersed in thesaturated liquid coolant. The method can include transporting thetwo-phase bubbly flow including the first amount of heat and the secondamount of heat away from the first and second devices. The first andsecond amounts of heat can be rejected to a heat rejection loop bydirecting the two-phase bubbly flow through a heat exchanger in thermalcommunication with the heat rejection loop.

Additional objects and features of the invention are introduced below inthe Detailed Description and shown in the drawings. While multipleembodiments are disclosed, still other embodiments will become apparentto those skilled in the art from the following Detailed Description,which shows and describes illustrative embodiments. As will be realized,the disclosed embodiments are susceptible to modifications in variousaspects, all without departing from the scope of the present disclosure.Accordingly, the drawings and detailed description are to be regarded asillustrative in nature and not restrictive.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described in the Detailed Descriptionbelow. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intendedthat this Summary be used to limit the scope of the claimed subjectmatter. Furthermore, the claimed subject matter is not limited toimplementations that solve any or all disadvantages noted in any part ofthis disclosure.

BRIEF DESCRIPTIONS OF DRAWINGS

FIG. 1 shows a front perspective view of a cooling apparatus installedon a plurality of servers arranged in eight racks in a data center.

FIG. 2A shows a rear view of the cooling apparatus of FIG. 1.

FIG. 2B shows a detailed view of a portion of the cooling apparatus ofFIG. 2A, where the pump, reservoir, heat exchanger, manifolds of theprimary cooling loop, and sections of flexible tubing connectingparallel cooling lines to the manifolds are visible.

FIG. 3 shows a left side view of the cooling apparatus of FIG. 1, wherethe pump, reservoir, heat exchanger, pressure regulator, first bypass, aportion of the primary cooling loop, and sections of flexible tubingconnecting parallel cooling lines to the inlet and outlet manifolds arevisible.

FIG. 4 shows an inlet manifold and an outlet manifold of the coolingapparatus and sections of flexible tubing with quick-connect fittingsconnecting parallel cooling lines to the inlet and outlet manifolds.

FIG. 5 shows a top perspective view of a server with its lid removed anda portion of a cooling apparatus installed within the server, thecooling apparatus having two heat sink modules mounted onvertically-oriented processors within the server, the heat sink modulesarranged in a series configuration and fluidly connected with sectionsof flexible tubing to transport coolant from an outlet port of a firstheat sink module to an inlet port of a second heat sink module.

FIG. 6 shows a top view of a server with its lid removed and a portionof a cooling apparatus installed within the server, the coolingapparatus including two heat sink modules mounted onhorizontally-oriented processors within the server, the heat sinkmodules arranged in a series configuration and held down with mountingbrackets and fluidly connected with a section of flexible tubing totransport coolant from an outlet port of a first heat sink module to aninlet port of a second heat sink module.

FIG. 7 shows a cooling assembly including a heat sink module, a firstsection of flexible tubing fluidly connected to an inlet port of theheat sink module, and a second section of flexible tubing fluidlyconnected to an outlet port of the heat sink module.

FIG. 8 shows a plot of power consumption versus time for a computer roomwith forty active dual-processor servers initially cooled by a CRAC andthen cooled by the CRAC and a cooling apparatus as described herein,where the cooling apparatus provides substantial reductions in overallpower consumption despite being installed on just ten of the fortyservers in the computer room.

FIG. 9 shows a front perspective view of a redundant cooling apparatusinstalled on eight racks of servers in a data center where the redundantcooling apparatus includes a first independent cooling system as shownin FIG. 1 and a second independent cooling system as shown in FIG. 1.

FIG. 10 shows a rear view of the redundant cooling apparatus of FIG. 9.

FIG. 11A shows a schematic of a cooling apparatus having one heat sinkmodule mounted on a heat-generating surface and fluidly connected to aprimary cooling loop, the cooling apparatus having a first bypassincluding a first pressure regulator upstream of a heat exchanger and asecond bypass including a second pressure regulator.

FIG. 11B shows the schematic of FIG. 11A with the primary cooling loopidentified by dashed lines.

FIG. 11C shows the schematic of FIG. 11A with the first bypassidentified by dashed lines.

FIG. 11D shows the schematic of FIG. 11A with the second bypassidentified by dashed lines.

FIG. 12A shows a schematic of a cooling apparatus having one heat sinkmodule mounted on a heat source and a pressure regulator locateddownstream of a heat exchanger in a first bypass.

FIG. 12B shows a schematic of a cooling apparatus having two pumpsarranged in parallel for redundancy in case one pump fails.

FIG. 12C shows a schematic of a cooling apparatus having a three-wayvalve at a junction between a primary cooling loop and a bypass.

FIG. 12D shows a schematic of a cooling apparatus having a three-wayvalve at a junction between a primary cooling loop and a bypass, wherethe bypass includes a heat exchanger.

FIG. 12E shows a schematic of a cooling apparatus including a bypass anda primary cooling loop where the primary cooling loop includes a heatsink module with an internal bypass containing a pressure regulator.

FIG. 12F shows a schematic of a cooling apparatus having a primarycooling loop and a bypass containing a pressure regulator, the primarycooling loop including a reservoir, pump, and heat sink module.

FIG. 12G shows a schematic of a cooling apparatus where a primarycooling loop includes a reservoir, a pump, and a heat sink module withan internal bypass containing a pressure regulator.

FIG. 12H shows a schematic of a cooling apparatus including a pump, areservoir, and a heat sink module that is configured to mount on a heatsource or be mounted in thermal communication with a heat source.

FIG. 12I shows a schematic of a cooling apparatus including a pump, suchas a variable speed pump, and a heat sink module configured to mount ona heat source or be mounted in thermal communication with a heat source.

FIG. 12J shows a schematic of a cooling apparatus with a primary coolingloop, a first bypass, and a second bypass, where the primary coolingloop includes a first pump, and the first bypass includes a second pump.

FIG. 12K shows a schematic of a cooling apparatus with a primary coolingloop, a first bypass, and a second bypass, where the primary coolingloop includes a first pump, and the second bypass includes a secondpump.

FIG. 12L shows a schematic of a cooling apparatus with a primary coolingloop, a first bypass, and a second bypass, where the primary coolingloop includes a first pump, the first bypass includes a second pump, andthe second bypass includes a third pump.

FIG. 12M shows a schematic of a cooling apparatus with a primary coolingloop, a first bypass, and a second bypass, where the first bypassincludes a first heat exchanger, and the second bypass includes a secondheat exchanger.

FIG. 12N shows a schematic of a cooling apparatus having a primarycooling loop, a first bypass, and a second bypass, where the firstbypass and second bypass merge upstream of a reservoir.

FIG. 12O shows a schematic of a cooling apparatus having a primarycooling loop, a first bypass, and a second bypass, where the firstbypass and second bypass merge upstream of a reservoir and upstream of aheat exchanger.

FIG. 12P shows a schematic of a cooling apparatus having a primarycooling loop with redundant parallel pumps, a first bypass, and a secondbypass, where the first bypass is fluidly connected to a heat exchangerthat can be a dry cooler.

FIG. 12Q shows a schematic of a cooling apparatus having a primarycooling loop and a bypass, where the bypass is connected to a heatexchanger that can be a dry cooler.

FIG. 12R shows a schematic of a preferred cooling apparatus having aprimary cooling loop, a first bypass, and a second bypass, where thefirst bypass includes a liquid-to-liquid heat exchanger fluidlyconnected to an external heat exchanger located outside of a room wherethe cooling apparatus is located, the external heat exchanger beingconnected to the heat exchanger by an external heat rejection loophaving a pump configured to circulate external cooling fluid, such as awater-glycol mixture, through the external heat rejection loop.

FIG. 12S shows a schematic of a cooling apparatus having a primarycooling loop, a first bypass, and a second bypass, where the firstbypass includes a first heat exchanger, and where the primary coolingloop includes two series-connected heat sink modules with a second heatexchanger fluidly connected between the heat sink modules to reducequality of the flow to avoid formation of slug flow in the primarycooling loop between the series-connected heat sink modules.

FIG. 12T shows a schematic of a cooling apparatus configured to cool tworacks of servers, the cooling apparatus including an inlet manifold andan outlet manifold for each rack of servers, where a plurality of heatsink modules are fluidly connected in series and parallel arrangementsbetween each inlet and outlet manifold to cool processors within theservers.

FIG. 13 shows a schematic of a cooling apparatus including a filterlocated between a reservoir and a pump in a primary cooling loop.

FIG. 14A shows a schematic of a cooling apparatus having three heat sinkmodules arranged in a series configuration on three surfaces to becooled.

FIG. 14B shows a representation of coolant flowing through three heatsink modules connected in series by lengths of tubing, similar to theconfigurations shown in FIGS. 14A and 15, and shows corresponding plotsof saturation temperature, liquid coolant temperature, pressure, andquality (x) versus distance, where quality increases, pressuredecreases, liquid coolant temperature decreases, and T_(sat) decreasesthrough the second and third series-connected heat sink modules.

FIG. 14C shows a representation of coolant flowing through three heatsink modules connected in series by lengths of tubing, similar to FIG.14B, except that the coolant does not reach its saturation temperatureuntil the second heat sink module and is therefore liquid coolant untilit transitions to two-phase bubbly flow within the second heat sinkmodule.

FIG. 15 shows a portion of a primary cooling loop of a coolingapparatus, where the cooling loop includes three series-connected heatsink modules mounted on three surfaces to be cooled and connected bysections of flexible tubing where a single-phase liquid coolant isprovided to a first heat sink module, and due to heat transfer withinthe first module, two-phase bubbly flow is transported from the firstmodule to the second module, and due to heat transfer within the secondmodule, higher quality two-phase bubbly flow is transported from thesecond module to the third module, and due to heat transfer within thethird module, even higher quality two-phase bubbly flow is transportedout of the third module.

FIG. 16 shows a schematic of a cooling apparatus having a primarycooling loop, a first bypass, and a second bypass, where the primarycooling line includes three parallel cooling lines where each parallelcooling line includes three heat sink modules fluidly connected inseries.

FIG. 17 shows a schematic of a redundant cooling apparatus having aredundant heat sink module mounted on a surface to be cooled, theredundant heat sink module having a first independent coolant pathwayfluidly connected to a first independent cooling system and a secondindependent coolant pathway fluidly connected to a second independentcooling system.

FIG. 18 shows a schematic of a redundant cooling apparatus having afirst independent cooling apparatus and a second independent coolingapparatus, where each of the independent cooling apparatuses has twoparallel cooling lines where each parallel cooling line is fluidlyconnected to three redundant heat sink modules arranged in series, whereeach redundant heat sink module has a first independent coolant pathwayfluidly connected to the first independent cooling apparatus and asecond independent coolant pathway fluidly connected to the secondindependent cooling apparatus.

FIG. 19 shows a top view of a redundant cooling apparatus installed in adata center having twenty racks of servers, the redundant cooling systemhaving a first independent cooling apparatus and a second independentcooling apparatus, both connected to heat exchangers located inside ofthe room where the servers are located, the fluid connections of thefirst independent cooling apparatus depicted with dashed lines and thefluid connections of the second independent cooling apparatus depictedwith solid lines.

FIG. 20 shows a top view of a redundant cooling apparatus installed in adata center having twenty racks of servers, the redundant cooling systemhaving a first independent cooling apparatus and a second independentcooling apparatus, both connected to heat exchangers located outside ofthe room where the data center is located, the fluid connections of thefirst independent cooling apparatus depicted with dashed lines and thefluid connections of the second independent cooling apparatus depictedwith solid lines.

FIG. 21 shows a top perspective view of a compact heat sink module forcooling a heat source.

FIG. 22 shows a top view of a heat sink module in FIG. 21, the heat sinkmodule further including a first compression fitting installed on aninlet port of the heat sink module, a second compression fittinginstalled on an outlet port of the heat sink module, and a plurality offasteners arranged near a perimeter of the heat sink module andaccording to a mounting pattern for mounting the heat sink module to aheat-providing surface.

FIG. 23 shows a bottom perspective view of the heat sink module of FIG.21 showing an inlet port, outlet port, outlet chamber, mounting holes,dividing member, and a plurality of orifices in the dividing member, aswell as a sealing member installed within a continuous channelcircumscribing the outlet chamber of the heat sink module.

FIG. 24 shows a bottom view of the heat sink module of FIG. 21 showingan array of orifices having staggered columns and staggered rows toprevent flow stagnation regions on a surface to be cooled.

FIG. 25 shows a side cross-sectional view of the heat sink module ofFIG. 24 taken along section B-B and showing an inlet port, an inletpassage, an inlet chamber, a plurality of orifices, a dividing member,and an outlet chamber within the heat sink module.

FIG. 26 shows a side cross-sectional view of the heat sink module ofFIG. 24 taken along section B-B with the heat sink module mounted on athermally conductive base member and showing central axes of severalorifices, jet heights, and bubble formation within the outlet chamberproximate the surface to be cooled of the thermally conductive basemember where a portion of the liquid coolant changes to vapor.

FIG. 27 shows a side cross-sectional view of the heat sink module ofFIG. 24 taken along section B-B with the heat sink module mounteddirectly on a computer processor located on a motherboard and showingcentral axes of several orifices.

FIG. 28 shows a side cross-sectional view of the heat sink module ofFIG. 24 taken along section B-B with the heat sink module mounted on athermally conductive base member that is bonded to a processor by alayer of thermal interface material, the microprocessor beingelectrically connected to a motherboard.

FIG. 29 shows a side cross-sectional view of the heat sink module ofFIG. 24 taken along section A-A and showing an outlet port, an outletpassage, an outlet chamber, a dividing member, and a plurality oforifices within the heat sink module.

FIG. 30 shows a side cross-sectional view of the heat sink module ofFIG. 24 taken along section A-A, with the heat sink module mounted on athermally conductive base member and sealed by a sealing member, thefigure showing bubbles forming within the outlet chamber proximate aheated surface of the conductive base member where a portion of thecoolant changes from liquid phase to vapor phase upon interacting withthe heated surface thereby forming two-phase bubbly flow, which exitsthe heat sink module through the outlet port.

FIG. 31 shows a cross-sectional top view of the heat sink module of FIG.21 taken along section C-C shown in FIG. 25, the cross-section passinghorizontally through the dividing member of the heat sink module toexpose an array of orifices within the heat sink module, the orifices inthe array being arranged according to staggered columns and staggeredrows to prevent flow stagnation regions on a surface to be cooled.

FIG. 32 shows a top view of a surface to be cooled within an outletchamber of a heat sink module of FIG. 21 taken along section D-D shownin FIG. 30, where an array of jet streams originating from the array oforifices in the heat sink module are impinging non-perpendicularly onthe surface to be cooled, thereby creating a directional flow of coolantfrom left to right across the surface to be cooled, the directional flowfilling the outlet chamber and traveling toward and exiting from anoutlet port of the heat sink module.

FIG. 33 shows a bottom view of a heat sink module having a firstplurality of orifices and a second plurality of orifices, the secondplurality of orifices being configured to deliver a plurality ofanti-pooling jet streams into the outlet chamber to promote directionalflow within the outlet chamber and to prevent pooling on the surface tobe cooled near a rear wall of the outlet chamber.

FIG. 34 shows a side cross-sectional view of the heat sink module ofFIG. 33 taken along section B-B, the side view showing an inlet port, aninlet passage, an inlet chamber, a plurality of orifices, an outletchamber, and an anti-pooling orifice within the heat sink module.

FIG. 35 shows a detailed view of a portion of the heat sink module ofFIG. 34 highlighting the anti-pooling orifice that extends from theinlet chamber to a rear wall of the outlet chamber and is configured todeliver an anti-pooling jet stream proximate a rear wall of the outletchamber to prevent pooling on the surface to be cooled.

FIG. 36 shows a side cross-sectional view of the heat sink module ofFIG. 33 taken along section B-B, with the heat sink module sealedagainst a thermally conductive base member and showing central axes of aplurality of orifices and an anti-pooling orifice located near a rearwall of the outlet chamber.

FIG. 37 shows a side cross-sectional view of the heat sink module ofFIG. 33 taken along section A-A and showing an outlet port, an outletpassage, an inlet chamber, an outlet chamber, a plurality of orifices,and an anti-pooling orifice.

FIG. 38 shows a side cross-sectional view of the heat sink module ofFIG. 33 taken along section A-A, with the heat sink module sealedagainst a thermally conductive base member, the figure showing coolantbeing introduced to an outlet chamber as a plurality of jet streams ofcoolant, a portion of liquid coolant changing phase upon absorbing heatfrom the surface to be cooled thereby forming a directional flow oftwo-phase bubbly flow that exits the heat sink module through an outletport.

FIG. 39 shows a top view of a heat sink module of FIG. 33.

FIG. 40 shows a side cross-sectional view of the heat sink module ofFIG. 39 taken along section B-B and showing the location of section C-Cpassing through an inlet chamber and the location of section D-D passingthrough an outlet chamber.

FIG. 41 shows a front view of the heat sink module of FIG. 33 showing anupwardly angled inlet port and an upwardly angle outlet port.

FIG. 42 shows a left side view of the heat sink module of FIG. 33showing an outlet port and an inlet port arranged at an angle of α withrespect to a mounting surface of the heat sink module, the angleconfigured to permit ease of assembly within a crowded server housing orother constrained installation.

FIG. 43 shows a top cross-sectional view of the heat sink module of FIG.39 taken along section C-C shown in FIG. 42, the top view showing theinlet port, inlet passage, inlet chamber, top surface of the dividingmember, and inlets of the plurality of orifices and plurality ofanti-pooling orifices.

FIG. 44 shows a cross-sectional bottom view of the heat sink module ofFIG. 39 taken along section D-D shown in FIG. 42, the bottom viewshowing the outlet port, outlet passage, outlet chamber, bottom surfaceof the dividing member, and outlets of the plurality of orifices andplurality of anti-pooling orifices.

FIG. 45 shows a bottom view of a heat sink module having a plurality ofboiling-inducing members extending from the dividing member into theoutlet chamber.

FIG. 46 shows a side cross-sectional view of the heat sink module ofFIG. 45 taken along section B-B, the side view showing an inlet port, aninlet passage, an inlet chamber, a plurality of orifices, a dividingmember, and a plurality of boiling-inducing members extending from thedividing member into the outlet chamber.

FIG. 47 shows a side cross-sectional view of the heat sink module ofFIG. 45 taken along section B-B with the heat sink module mounted on athermally conductive base member and showing central axes of theplurality of orifices.

FIG. 48 shows a detailed view of a portion of the heat sink module shownin FIG. 46, the detailed view showing three boiling inducing membersextending from a bottom surface of the dividing member into the outletchamber and an orifice extending from the inlet chamber to the outletchamber, a flow clearance being provided between a tip of eachboiling-inducing member and a surface to be cooled.

FIG. 49 shows a side cross-sectional view of the heat sink module ofFIG. 45 taken along section A-A, the side view showing an outlet port,an outlet passage, an inlet chamber, an outlet chamber, a plurality oforifices, an anti-pooling orifice, a plurality of boiling-inducingmembers, and a dividing member.

FIG. 50 shows a side cross-sectional view of the heat sink module ofFIG. 45 taken along section A-A, the heat sink module being mounted on athermally conductive base member, the figure showing central axes of theplurality of orifices and an anti-pooling orifice.

FIG. 51A shows a top perspective view of a redundant heat sink modulehaving a first independent coolant pathway and a second independentcoolant pathway.

FIG. 51B shows a top view of the redundant heat sink module of FIG. 51A,where the first independent coolant pathway and the second independentcoolant pathway are represented by dashed lines, where the firstindependent coolant pathway passes through a first region near a middleof the module, and where the second independent coolant pathway passesthrough a second region beyond a perimeter of the first region.

FIG. 51C shows a top view of the redundant heat sink module of FIG. 51Awith compression fittings installed on the inlet and outlet ports.

FIG. 51D shows a bottom view of the redundant heat sink module of FIG.51A, where the first independent coolant pathway includes an array oforifices arranged in a first region located near a middle of the heatsink module, and where the second independent coolant pathway includesan array of orifices arranged in a second region circumscribing thefirst region, and where a first sealing member is configured to providea liquid-tight seal between the first and second independent coolantpathways.

FIG. 51E shows a top view of the heat sink module of FIG. 51A.

FIG. 51F shows a cross-sectional side view of the redundant heat sinkmodule of FIG. 51A taken along section A-A shown in FIG. 51E, the figureshowing a first inlet port, a first inlet passage, a first inletchamber, a first outlet chamber, a first plurality of orifices, aportion of a second outlet chamber, and a second outlet port.

FIG. 51G shows a side cross-sectional side view of the redundant heatsink module of FIG. 51A taken along section B-B shown in FIG. 51E, thefigure showing a second inlet port, a second inlet passage, one orificeof a second plurality of orifices, a first plurality of orifices, oneanti-pooling orifice of a first plurality of anti-pooling orifices, afirst outlet chamber, a portion of a second outlet chamber, and a firstoutlet port.

FIG. 51H shows a side view of the redundant heat sink module of FIG. 51Ashowing upwardly angled ports configured to ease installation in acrowded server housing or other constrained installation.

FIG. 51I shows a cross-sectional rear view of the redundant heat sinkmodule of FIG. 51A taken along section C-C shown in FIG. 51H, the figureshowing a first inlet chamber, a first outlet chamber, and a firstplurality of orifices associated with a first independent coolantpathway and a second inlet chamber, a second outlet chamber, and asecond plurality of orifices associated with a second independentcoolant pathway.

FIG. 51J shows a top view of the redundant heat sink module of FIG. 51A.

FIG. 51K shows a side cross-sectional view of the redundant heat sinkmodule of FIG. 51A taken along section D-D shown in FIG. 51J, the figureshowing a significant portion of the first independent coolant pathway.

FIG. 51L shows a top view of the redundant heat sink module of FIG. 51A.

FIG. 51M shows a side cross-section view of the redundant heat sinkmodule of FIG. 51A taken along section E-E of FIG. 51L, the figureshowing a significant portion of the second independent coolant pathway.

FIG. 51N is a top view of the redundant heat sink module of FIG. 51A andshows flow vectors in a first independent coolant pathway and flowvectors in a second independent coolant pathway.

FIG. 51O is a top view of the redundant heat sink module of FIG. 51A andshows a first independent coolant pathway having a first inlet port anda first outlet port and a second independent coolant pathway having asecond inlet port and a second outlet port, where coolant enters thefirst inlet port as liquid flow and exits the first outlet port astwo-phase bubbly flow, and where coolant enters the second inlet port asliquid flow and exits the second outlet port as two-phase bubbly flow.

FIG. 51P is a top view of the redundant heat sink module of FIG. 51A andshows a first coolant pathway having a first inlet port and a firstoutlet port and a second coolant pathway having a second inlet port anda second outlet port, where coolant enters the first inlet port asliquid flow and exits the first outlet port as liquid flow, and wherecoolant enters the second inlet port as liquid flow and exits the secondoutlet port as two-phase bubbly flow.

FIG. 51Q is a top view of the redundant heat sink module of FIG. 51A andshows a first coolant pathway having a first inlet port and a firstoutlet port and a second coolant pathway having a second inlet port anda second outlet port, where coolant enters the first inlet port asliquid flow and exits the first outlet port as two-phase bubbly flow,and where coolant enters the second inlet port as liquid flow and exitsthe second outlet port as liquid flow.

FIG. 52A shows two redundant heat sink modules mounted on a thermallyconductive base member, where two sink modules are provided forredundancy and/or increased heat transfer capability.

FIG. 52B shows two heat sink modules mounted on a thermally conductivebase member, where two sink modules are provided for redundancy and/orincreased heat transfer capability.

FIG. 53 shows a top perspective view of a redundant heat sink modulehaving side-by-side independent coolant pathways.

FIG. 54 shows a bottom perspective view of a redundant heat sink modulemounted to a planar, thermally conductive base member with fasteners.

FIG. 55 shows a top perspective view of a thermally conductive basemember having a surface to be cooled and an array of boiling-inducingmembers extending from the surface to be cooled, the array ofboiling-inducing members configured to fit within an inner perimeter ofan outlet chamber of a heat sink module when the heat sink module ismounted on the thermally conductive base member.

FIG. 56 shows a top perspective view of a motherboard of a serverincluding microprocessors and a plurality of vertically arranged memorymodules that are parallel and offset, where a heat sink module can bemounted on top of each microprocessor.

FIG. 57 shows a top perspective view of a server including a pluralityof vertically arranged memory modules that are parallel and offset.

FIG. 58 shows two-phase flow regimes, including (a) bubbly flow with afirst number density of bubbles, (b) bubbly flow with a second numberdensity of bubbles that is greater than the first number density ofbubbles, (c) slug flow, (d) churn flow, and (e) annular flow.

FIG. 59A shows a flow regime map for a steam-water system withρ_(hquid)*j_(liquid) ² on the x-axis and ρ_(vapor)*j_(vapor) ² on they-axis.

FIG. 59B shows two-phase flow regimes for coolant plotted on voidfraction versus mass flux axes.

FIG. 60 shows a flow boiling curve for water where heat transfer rate isplotted as a function of excess temperature.

FIG. 61 shows a boiling curve for water at one atmosphere and shows anonset of nucleate boiling, an inflection point, the point of criticalheat flux, and the Leidenfrost point.

FIG. 62 shows possible orifice configurations for a heat sink module,including (a) a regular rectangular jet array, (b) a regular hexagonaljet array with staggered columns and staggered rows, and (c) a circularjet array.

FIG. 63 shows a top view of a heated surface covered by coolant, thecoolant having regions of vapor coolant and wetted regions of liquidcoolant in contact with the heated surface, where a three-phase contactline length is measured as a sum of all curves where liquid coolant,vapor coolant, and the heated surface are in mutual contact on theheated surface.

FIG. 64 shows a plot of power consumption versus junction temperaturefor a processor at a static condition and at dynamic conditions withswitching speeds of 1.6 GHz and 2.4 GHz.

FIG. 65 shows a heat sink module with an insertable orifice plateinstalled within a module body, where a sealing member is providedbetween the insertable orifice plate and the module body.

FIG. 66 shows a side cross-sectional view of a motherboard having afirst microprocessor, a second microprocessor, a first finned heat sinkarranged on top of the first microprocessor, a second finned heat sinkarranged on top of the second microprocessor, and a cooling apparatus,where the cooling apparatus includes a heat sink module mounted on athermally conductive member that extends from the first finned heat sinkto the second heat sink module.

FIG. 67 shows a side cross-sectional view of a motherboard having afirst microprocessor, a second microprocessor, and a cooling system,where the cooling system includes a heat sink module mounted on athermally conductive member that extends from the first microprocessorto the second microprocessor.

FIG. 68 shows a schematic of a cooling apparatus having a primarycooling loop, a bypass, and an independent heat rejection loop having apump and a heat exchanger, where the primary cooling loop and theindependent heat rejection loop are both fluidly connected to a commonreservoir.

FIG. 69 shows a schematic of a redundant cooling apparatus having afirst cooling apparatus, a second cooling apparatus, and a heatrejection loop having a pump and a heat exchanger, where the firstcooling apparatus, the second cooling apparatus, and the heat rejectionloop are fluidly connected to a common reservoir.

FIG. 70 shows a schematic of a redundant cooling apparatus having aredundant heat sink module mounted on a heat source, the redundant heatsink module fluidly connected to a first cooling apparatus and a secondcooling apparatus, the first and second cooling apparatuses sharing acommon reservoir.

FIG. 71 shows a schematic of a cooling apparatus having a primarycooling loop with a pump, a heat exchanger, a heat sink module mountedon a heat source, a reservoir, and a bypass, the bypass having apressure regulator configured to control a pressure differential betweenan inlet port and an outlet port of the heat sink module.

FIG. 72 shows a schematic of a cooling apparatus having a primarycooling loop with redundant, parallel pumps and check valves, areservoir, a heat exchanger, a heat sink module mounted on a heatsource, and a bypass, the bypass having a pressure regulator configuredto control a pressure differential between an inlet port and an outletport of the heat sink module.

FIG. 73 shows a cross-sectional view of a first heat sink module fluidlyconnected to a second heat sink module by a section of flexible tubing,where single-phase flow delivered to an inlet chamber of the first heatsink module becomes two-phase bubbly flow within an outlet chamber ofthe first heat sink module due to heat being transferred from a firstsurface to be cooled to the flow, where flexible tubing transports thetwo-phase bubbly flow from an outlet port of the first heat sink moduleto an inlet port of a second heat sink module, where the two-phasebubbly flow is delivered to an inlet chamber of the second heat sinkmodule and passes as a plurality of jet streams through a plurality oforifices within the second heat sink module, the jet streams configuredto impinge against a second surface to be cooled and absorb heat fromthe second surface to be cooled.

FIG. 74 shows a portable cooling device that includes a plurality ofheat sink modules mounted on a portable layer, the portable layer beingconformable to a contoured heated surface or rigid and including one ormore inlet connections and one or more outlet connections that can beconnected to a cooling apparatus that delivers a flow of pressurizedcoolant to the portable cooling device to permit cooling of the heatedsurface through latent heating of the coolant within the plurality ofheat sink modules.

FIG. 75 shows a schematic of a preferred cooling apparatus having aprimary cooling loop, a first bypass, and a second bypass, where thefirst bypass includes a liquid-to-liquid heat exchanger fluidlyconnected to an external heat exchanger located outside of a room wherethe cooling apparatus is located, the external heat exchanger beingconnected to the heat exchanger by an external heat rejection loophaving a pump configured to circulate external cooling fluid, such as awater-glycol mixture, through the external heat rejection loop, theexternal heat exchanger being an air-to-liquid heat exchanger.

FIG. 76 shows a schematic of a cooling apparatus having a primarycooling loop, a first bypass, and a second bypass, where the firstbypass includes a liquid-to-liquid heat exchanger fluidly connected to aheat rejection loop, the heat rejection loop being a supply of chilledwater from a building in which the cooling apparatus is installed.

FIG. 77 shows a schematic of a preferred cooling apparatus having aprimary cooling loop, a first bypass, and a second bypass, where thefirst bypass includes a liquid-to-liquid heat exchanger fluidlyconnected to an external heat exchanger located outside of a room wherethe cooling apparatus is located, the external heat exchanger beingconnected to the heat exchanger by an external heat rejection loophaving a pump configured to circulate external cooling fluid, such as awater-glycol mixture, through the external heat rejection loop, theexternal heat exchanger being an liquid-to-liquid heat exchanger beingconnected to a supply of chilled water from a building in which thecooling apparatus is installed.

FIG. 78 shows a schematic of a cooling apparatus that is configured toallow cooling lines to be added or removed during operation of thecooling apparatus without causing unstable two-phase flow in theapparatus.

FIG. 79 shows a schematic of a cooling apparatus having an inletmanifold, an outlet manifold, a pressure regulator fluidly connectedbetween the inlet manifold and the outlet manifold, and thirty coolinglines extending from the inlet manifold to the outlet manifold.

FIG. 80 shows a schematic of a cooling apparatus having a first inletmanifold, a first outlet manifold, and a first set of thirty coolinglines associated with a first server rack, the cooling apparatus alsohaving a second inlet manifold, a second outlet manifold, and a secondset of thirty cooling lines associated with a second server rack, wherea fluid distribution unit provides a flow of coolant to the first andsecond inlet manifolds, the fluid distribution unit including a pump anda reservoir.

FIG. 81 shows a representation of a preferred cooling apparatus having aflow of single-phase liquid coolant being pumped from a pump outlet, aflow of subcooled single-phase liquid coolant passing through a firstbypass containing a heat exchanger and a first pressure regulator, aflow of single-phase liquid coolant passing through a second bypasscontaining a second pressure regulator, a flow of single-phase liquidcoolant passing through a cooling line into a heat sink module andexiting the heat sink module as two-phase bubbly flow due to heattransfer from a heat-providing surface to the coolant, a mixed flow ofsingle-phase liquid coolant and two-phase bubbly flow passing through areturn line to a reservoir, where vapor in the two-phase bubbly flow iscondensed back to liquid in the return line due to heat transfer fromthe two-phase bubbly flow to the single-phase liquid coolant resultingin sensible heating of the single-phase liquid coolant.

FIG. 82 shows a representation of a cooling apparatus having a flow ofsingle-phase liquid coolant being withdrawn from a reservoir and pumpedfrom a pump outlet, a flow of single-phase liquid coolant passingthrough a bypass containing a pressure regulator, a flow of single-phaseliquid coolant passing through a cooling line into a heat sink moduleand exiting the heat sink module as two-phase bubbly flow due to heattransfer from a heat-providing surface to the coolant, a mixed flow ofsingle-phase liquid coolant and two-phase bubbly flow passing through areturn line to the reservoir, where vapor in the two-phase bubbly flowis condensed back to liquid in the return line and in the reservoir dueto heat transfer from the two-phase bubbly flow to subcooled liquidcoolant in the reservoir.

FIG. 83 shows a representation of a cooling apparatus having a flow ofsingle-phase liquid coolant being withdrawn from a reservoir pumped froma pump outlet, a flow of subcooled single-phase liquid coolant passingthrough a bypass containing a heat exchanger and a first pressureregulator, a flow of single-phase liquid coolant passing through acooling line into a heat sink module and exiting the heat sink module astwo-phase bubbly flow due to heat transfer from a heat-providing surfaceto the coolant, mixing of the two-phase bubbly flow and the flow ofsubcooled single-phase liquid coolant in the reservoir, where vapor inthe two-phase bubbly flow is condensed back to liquid in the reservoirdue to heat transfer from the two-phase bubbly flow to the subcooledsingle-phase liquid coolant.

FIG. 84 shows a top perspective view of two series-connected heat sinkmodules installed on top of microprocessors within a server housing,each heat sink module held in place by a mounting bracket secured tomounting holes in the motherboard using threaded fasteners, the heatsink modules being fluidly connected with flexible tubing.

FIG. 85 shows a top view of a heat sink module mounted on amicroprocessor in a server, the heat sink module being secured to amotherboard of the server by an S-shaped bracket that permits variablepositioning of the heat sink module on a top surface of themicroprocessor for ease of routing sections of flexible tubing thattransport coolant to and from the heat sink module.

FIG. 86 shows a top perspective view of a heat sink module mounted ontop of a microprocessor of a motherboard with an S-shaped bracket priorto installation of flexible cooling lines to and from an inlet port andan outlet port, respectively, of the heat sink module.

FIG. 87 shows a top view of the motherboard of FIG. 86.

FIG. 88 shows an enlarged top perspective view of the motherboard ofFIG. 86 showing the heat sink module mounted on top of themicroprocessor.

FIG. 89 shows an enlarged top view of the motherboard of FIG. 86 showingthe heat sink module mounted on top of the processor.

FIG. 90 shows a top view of a heat sink module mounted on a thermallyconductive base member with an S-shaped mounting bracket with slottedmounting holes.

FIG. 91 shows a top view of a heat sink module with an S-shaped mountingbracket with slotted mounting holes.

FIG. 92 shows a front perspective view of a cooling apparatus withredundant pumps with automatic failover circuitry, a reservoir, and abypass with a pressure regulator and a heat exchanger, the heatexchanger configured to connect to an external heat rejection loop.

FIG. 93 shows a right side view of the cooling apparatus of FIG. 92.

FIG. 94 shows a front view of the cooling apparatus of FIG. 92.

FIG. 95 shows an exploded view of the cooling apparatus of FIG. 92.

FIG. 96 shows an exploded view of the pump and shut-off valves of thecooling apparatus of FIG. 92.

FIG. 97 shows the heat exchanger of FIG. 92 having a first isolatedfluid pathway for transporting a dielectric coolant from a first bypassof the cooling apparatus and a second isolated fluid pathway fortransporting a glycol-water mixture from an external heat rejectionloop, the first and second isolated fluid pathways being in thermalcommunication within the heat exchanger.

FIG. 98 shows a top perspective view of two series-connected heat sinkmodules installed on top of operating processors within a server, wheresubcooled single-phase liquid coolant is delivered to a first heat sinkmodule wherein it absorbs sensible heat causing the temperature of thecoolant to rise, and where the single-phase liquid coolant is thentransported from the first module to the second heat sink module whereit absorbs additional sensible heat unit it reaches its saturationtemperature and thereafter absorbs latent heat resulting in formation oftwo-phase bubbly flow that can be transported out of the server.

FIG. 99 shows a top perspective view of two series-connected heat sinkmodules installed on top of operating processors within a server, wheresingle-phase liquid coolant is delivered to the first heat sink modulewherein it absorbs sensible heat until it reaches its saturationtemperature and thereafter absorbs latent heat resulting in formation oftwo-phase bubbly flow having a first quality, and where the two-phasebubbly flow having a first quality is then transported to a second heatsink module wherein it absorbs additional latent heat resulting inadditional bubble formation, thereby changing the two-phase bubbly flowto a second quality greater than the first quality.

, and where the single-phase liquid coolant is transported from thefirst module to the second module wherein the coolant reaches itssaturation temperature and latent heat transfer results in the formationof two-phase bubbly flow.

DETAILED DESCRIPTION

The cooling apparatuses 1 and methods described herein are suitable fora wide variety of applications, ranging from cooling electrical devicesto cooling mechanical devices to cooling chemical reactions and/orrelated devices and processes. Examples of electrical devices that canbe effectively cooled with the cooling apparatuses 1 and methods includedensely packed servers in data centers, computers in distributedcomputing clusters, medical imaging devices, electronic communicationsequipment in cellular networks, solar panels, high-power diode laserarrays, and electric vehicle components (e.g. battery packs, electricmotors, and power electronics). Examples of mechanical devices that canbe effectively cooled with the cooling apparatuses 1 and methods includeturbines, internal combustion engines, turbochargers, after-treatmentcomponents, and braking systems. Examples of chemical processes that canbe effectively cooled with the cooling apparatuses 1 includecondensation processes involving rotary evaporators or refluxdistillation condensers.

Compared to competing air or single-phase liquid cooling systems, thecooling apparatuses 1 and methods described herein are more efficient,have higher reliability, operate more safely, are less expensive, andhave lower operating noise. The cooling apparatuses 1 described hereinare suitable for retrofit on existing server designs or can beincorporated into new server or processor designs. Due to their highefficiency, modularity, flexible connections, small size, andhot-swappability, the cooling apparatuses 1 described herein redefinedesign constraints that have until now hampered the development of newelectronic devices. The cooling apparatuses 1 described herein allow thesize of electronic device housings to be significantly reduced whilereducing the risk of overheating of critical components and maintainingor even improving device performance by maintaining the device atconsistent operating temperatures.

In the case of servers 400 arranged in server racks 410, the coolingapparatus 1 described herein allows servers 400 to be arranged in closeproximity to neighboring servers in the same rack 410, as shown in FIGS.1-3, thereby allowing more servers to be installed and cooled per squarefoot of floor space in a data center 425. In addition, the fluiddistribution unit 10 of the cooling apparatus 1 has a small footprint ofabout 7 square feet, whereas a CRAC unit that it displaces may have afootprint of over 42 square feet. Consequently, installing the coolingapparatus 1 described herein instead of a CRAC unit frees up enoughfloor space to accommodate at least five additional racks 410 of denselypacked servers 400.

The cooling apparatus 1 described herein can be deployed in computerrooms and in large-scale data center applications. In otherapplications, the cooling apparatus 1 can be made in smaller sizessuitable for incorporation in automobiles, aircraft, and other vehicles,which may require cooling of batteries, inverters, and other electronicdevices. In still other applications, the cooling apparatus 1 can beminiaturized for use in laptop and tablet computers and in handheldmobile electronic devices. In such examples, coolant passageways fortransporting dielectric coolant 50 to a heat sink module 100 can beformed directly on a circuit board of the mobile device by any suitablemanufacturing process, such as 3D printing. Similarly, heat sink module100 can be formed directly on a processor, memory module, or otherelectronic component of the mobile device by, for example, 3D printing.

Using the methods described herein, a high-efficiency cooling apparatus1 for a wide variety of applications can be rapidly designed, optimized,manufactured, and installed. In some examples, additive-manufacturingprocesses can be used to rapidly manufacture heat sink modules 100 thatpermit consistent cooling of multiple device surfaces 12, even whenthose devices have non-uniform heat distributions on their surfaces,such as surfaces of multi-core microprocessors.

Due to their small size and flexible connections, the componentsdescribed herein can be discretely packaged in many existing machinesand devices that require efficient and reliable cooling of surfaces thatproduce high heat fluxes. For example, the cooling apparatuses 1described herein can be discretely packaged in personal computers orservers to cool computer processing units (CPUs), graphic processingunits (GPUs), and memory modules, in vehicles to cool battery packs,inverters, electric motors, in-dash entertainment and navigationsystems, display screens, and power electronics, and in medical imagingdevices to cool power supplies and other electronic components.

In data center applications, the cooling apparatuses 1 and methodsdescribed herein can provide local, efficient cooling of critical systemcomponents and, where the data center 425 is located in an officebuilding, can allow the ambient temperature of the office building toremain at a temperature that is comfortable for human occupants, whilestill permitting effective cooling of critical system components.Presently, competing air cooling systems use room air within an officebuilding to cool critical system components by employing small fans toblow air across finned surfaces of system components. As the systemcomponents (e.g. microprocessors) are more highly utilized, they beginto generate more heat. To provide additional cooling, there are only twooptions in an air cooling system. First, the mass flow rate of airacross the components can be increased to increase the heat transferrate, or second, the temperature of the room air can be reduced toprovide a larger temperature differential between the room air and thecomponent temperature, thereby increasing the heat transfer rate.Initially, fans speeds can be increased to provide higher flow rates ofroom air, which in turn provides higher heat transfer rates. However, atsome point, maximum fan speeds will be attained, at which point the flowrate of room air can no longer be increased. At this point, if criticalsystem components demand additional cooling (e.g. to prevent overheatingor failure), the only option in competing air cooling systems is todecrease the temperature of the room air by delivering larger volumetricflow rates of cool air from an air conditioning unit to the room toreduce the room temperature. This approach is highly inefficient andultimately results in discomfort for human occupants of the officebuilding, since larger volumetric flow rates of cool air eventuallycause the air temperature within the building to reach an uncomfortablycool temperature, which can diminish worker productivity.

Experimental Data

FIG. 8 shows a plot of experimental data showing power consumed versustime to cool a computer room 425 having forty active dual-processorservers 400. The left portion of the plot, extending from about 15 to390 minutes, shows power consumed by a CRAC tasked with cooling thecomputer room 425. From about 15 to 190 minutes, the servers 400 werefully utilized, and from about 240 to 360 minutes, the servers were atidle state. At about 390 minutes, the cooling apparatus 1 was activatedto assist the CRAC with cooling the servers 400. However, the heat sinkmodules 100 connected to the cooling apparatus 1 were only installed onmicroprocessors in 25% of the servers (ten of forty servers).Nevertheless, a dramatic reduction in power consumption was recorded.From 390 to 590 minutes, the cooling apparatus 1 conserved about 1.5 kWof power compared to the baseline idle state cooled by the CRAC only,and from about 625 to 840 minutes, the cooling apparatus 1 conservedabout 2 kW of power compared to the baseline fully utilized state cooledby the CRAC only. The reduction in power consumption measured in thisexperiment is expected to scale as more servers in the computer room areconnected to the cooling apparatus 1. Consequently, if heat sink modules100 of the cooling apparatus 1 were installed on microprocessors 415 ofall forty servers 400, reductions in power consumption of about 6 kW(i.e. 55%) and 8 kW (i.e. 67%) compared to the baseline idle andbaseline fully utilized states, respectively, are expected. Reductionsin power consumption of this magnitude can translate to significantsavings in annual operating expenses for computer room and data centeroperators.

Experimental tests have demonstrated that significantly higher heattransfer rates are achievable with the cooling apparatus 1 than withexisting single-phase pumped liquid systems. This higher heat transferrate can be attributed, at least in part, to establishing conditions inan outlet chamber 150 of the heat sink module 100 that promote boilingof the coolant proximate the surface to be cooled 12. Experimental testshave confirmed that the heat sink module 100 shown in FIG. 21 is capableof dissipating a heat load of about 500 thermal watts, and the redundantheat sink module 700 shown in FIG. 51A is capable of dissipating a heatload of about 800 thermal watts.

During testing, a heat sink module 100 was provided that contained aplurality of orifices 155 configured to provide impinging jets streams16 of coolant 50 directed against a surface to be cooled 12, as shown inFIG. 26. In a first test, the pressure in the outlet chamber 150 of theheat sink module 100 was set to establish a saturation temperature ofabout 95° C. for the coolant. In a second test, the pressure in theoutlet chamber 150 of the heat sink module 100 was set to establish asaturation temperature of about 74° C. for the coolant. The saturationtemperature of about 74° C. was chosen to substantially match the meantemperature of the heated surface (i.e. surface to be cooled 12) in thetest. The same flow rate of coolant was used for each test. During thesecond test, bubbles 275 were generated in the outlet chamber 150 withthe coolant having the lower saturation temperature. Such a phase changedid not occur in the outlet chamber 150 with coolant having the highersaturation temperature in the first test. Overall, the heat transferperformance increased by 80% with the lower saturation temperature (i.e.the second test) where bubbles were generated compared to the highersaturation temperature (i.e. the first test) where bubbles were notgenerated.

One benefit of the cooling technology described herein is the ability toefficiently cool local hot spots on a heat-generating device 12 (e.g.hot spots on microprocessors 415). For example, if just one core of agiven microprocessor 415 is more heavily utilized than other cores inthe same processor, and a plurality of jet streams of coolant aredirected at the surface of the microprocessor, more evaporation willoccur proximate the hot core, thereby increasing the local heat transferrate proximate the hot core relative to the cooler cores, and therebyself-regulating to maintain the entire surface 12 of the microprocessorat a more uniform temperature than is possible with purely single-phasecooling systems that are incapable of self-regulating. Because thecooling apparatus 1 is capable of self-regulating to cool local hotspots (e.g. by providing local increases in heat transfer rates throughevaporation), the entire cooling system can be operated at lower flowrate and pressure, which conserves energy, and still handle fluctuationsin processor temperature caused by variations in utilization. This is insharp contrast to existing liquid cooling systems that are not capableof self-regulating to cool local hot spots and must therefore beoperated at much higher flow rates and pressures to ensure adequatecooling of hot spots, for example, on microprocessors. In other words,existing liquid cooling systems must operate continuously at a settingthat is designed to handle a peak heat load to ensure the system iscapable of handling the peak heat load if it occurs. As a result, whenthe microprocessor is not being heavily utilized, which is quite often,existing systems operate at a pressure and flow rate that areconsiderably above where they would otherwise need to operate to handlea non-peak heat load. This approach needlessly consumes a significantamount of excess energy, and is therefore undesirable.

Two-Phase Flow

In some aspects, the cooling apparatuses 1 described herein can beconfigured to cool a heat-generating surface 12 by directing jet streams16 of coolant against the surface 12 and by flowing coolant 50 over thesurface 12, as shown in FIGS. 26 and 30. The terms “heat-generatingsurface,” “surface to be cooled,” “surface of the device,” “heatsource,” “heated surface,” “heat providing surface,” “device surface,”“component surface,” and “heat-producing surface” are used herein todescribe any surface 12 of a component or device that is at atemperature above ambient temperature, whether due to heat produced byor within the component or device or due to heat transferred to thecomponent or device from some other component or device that is inthermal communication with the surface 12. Within some components of thecooling apparatus 1, at least a portion of the coolant 50 can undergo aphase change from a liquid to a vapor in response to absorbing heat fromthe surface 12 of the device. The phase change can result in the coolant50 transitioning from a single-phase liquid flow to two-phase bubblyflow or from a two-phase bubbly flow having a first number density ofvapor bubbles to two-phase bubbly flow having a second number density ofvapor bubbles, where the second number density is higher than the firstnumber density. By initiating boiling proximate the surface 12 beingcooled, and taking advantage of the highly-effective heat transfermechanisms associated therewith, the cooling apparatuses 1 and methodsdescribed herein can deliver heat transfer rates that far exceed heattransfer rates attainable with traditional single-phase liquid coolingor air cooling systems. By providing dramatically increased heattransfer rates, the cooling apparatus 1 described herein is able to cooldevices far more efficiently than any other existing cooling apparatus,which translates to significantly lower power consumption by the coolingapparatus 1 and lower utility bills. Where the cooling apparatus 1 isused in a large scale cooling application, such as a data center, andreplaces a conventional air conditioning system, the cooling apparatuscan result in significant savings on utility bills for a data centeroperator.

When a heat-generating surface 12 exceeds the saturation temperature ofthe coolant 50, boiling of the coolant proximate (i.e. at or near) theheat-generating surface occurs. This can occur whether the bulk fluidtemperature of the coolant 50 is at or below its saturation temperature.If the bulk fluid temperature is below the saturation temperature of thecoolant 50, boiling is referred to as “local boiling” or “subcooledboiling.” If the bulk fluid temperature of the coolant is equal to thesaturation temperature, then “bulk boiling” is said to occur. Bubblesformed proximate the heat-generating surface 12 depart the surface 12and are transported by the bulk fluid, creating a flow of liquid fluidwith bubbles distributed therein, known as two-phase bubbly flow.Depending on the degree of subcooling, as the bubbly flow passes throughtubing, some or all of the bubbles in the bubbly flow may condense andcollapse as mixing of the fluid and bubbles occurs. As bubbles collapseback to liquid, the bulk fluid temperature rises. In saturated or bulkboiling, where the bulk fluid temperature is near the saturationtemperature, the bubbles 275 distributed in the fluid may not collapseas the bubbly flow passes through tubing and as mixing of the fluid andbubbles occurs.

Two-phase flow can be defined based on a volume fraction of vaporpresent in the flow, where the volume fraction of vapor in the flow(α_(vapor)) plus the volume fraction of liquid (α_(liquid)) in the flowis equal to one (α_(vapor)+α_(liquid)=1). The volume fraction of vapor(α_(vapor)) is commonly referred to as “void fraction” even though thevapor volume is filled with low density gas and no true voids exist inthe flow. The volume fraction within a tube, such as a section offlexible tubing 225 between two series-connected heat sink modules 100,can be calculated using the following equation:

α_(vapor) =A _(vapor) /A _(x)

where A_(x) is the total cross-sectional flow area at point x in thetube, and A_(vapor) is the cross-sectional area occupied by vapor atpoint x in the tube. The volumetric flux of vapor (j_(vapor)) in a flow51, also known as the “superficial velocity” of the vapor, can becalculated using the following equation:

j _(vapor)=(v _(vapor) ×A _(vapor))/A _(x)=α_(vapor) ×v _(vapor)

where v_(vapor) is the velocity of vapor in the tube. In some instances,the velocity of vapor (v_(vapor)) and the velocity of the liquid(v_(liquid)) in the flow may not be equal. This inequality in velocitiescan be described as a slip ratio and calculated using the followingequation:

S=v _(vapor) /v _(liquid)

Where the vapor velocity (v_(vapor)) and the liquid velocity(v_(liquid)) in the flow are equal, the slip ratio (S) is one. The flowquality is the flow fraction of vapor and is always between zero andone. Flow quality (x) is defined as:

x={dot over (m)} _(vapor) /{dot over (m)}={dot over (m)} _(vapor)/({dotover (m)} _(vapor) +{dot over (m)} _(liquid))

where {dot over (m)}_(vapor) is the mass flow rate of vapor in the tube,{dot over (m)}_(liquid) is the mass flow rate of liquid in the tube, andm is the total mass flow rate in the tube ({dot over (m)}={dot over(m)}_(vapor)+{dot over (m)}_(liquid)). The mass flow rate of liquid isdefined as:

{dot over (m)} _(liquid)=ρ_(liquid) ×v _(liquid) ×A _(liquid)

where ρ_(liquid) is the density of the liquid, and A_(liquid) is thecross-sectional area occupied by liquid at point x in the tube.Similarly, the mass flow rate of vapor is defined as:

{dot over (m)} _(vapor)=ρ_(vapor) ×v _(vapor) ×A _(vapor)

where ρ_(vapor) is the density of the vapor. The distribution of vaporin a two-phase flow of coolant 50, such as a two-phase flow of coolantwithin a heat sink module 100 mounted on a heat-generating surface 12,affects both the heat transfer properties and the flow properties of thecoolant 50. These properties are discussed in greater detail below.

A number of flow patterns or “flow regimes” have been observedexperimentally by viewing flows of two-phase liquid-vapor mixturespassing through transparent tubes. While the number and characteristicsof specific flow regimes are somewhat subjective, four principal flowregimes are almost universally accepted. These flow regimes are shown inFIG. 58 and include (1) bubbly flow, (2) slug flow, (3) churn flow, and(4) annular flow. FIG. 58( a) shows bubbly flow having a first numberdensity of bubbles, and FIG. 58( b) shows bubbly flow having a secondnumber density of bubbles where the second number density is greaterthan the first number density of FIG. 58( a). FIG. 58( c) shows slugflow. FIG. 58( d) shows churn or churn-turbulent flow. FIG. 58( e) showsannular flow. Beyond annular flow, the flow will transition throughwispy-annular flow before eventually reaching single-phase vapor flow.

Bubbly flow is generally characterized as individually dispersed bubbles275 transported in a continuous liquid phase. Slug flow is generallycharacterized as large bullet-shaped bubbles separated by liquid plugs.Churn flow is generally characterized as vapor flowing in a chaoticmanner through liquid, where the vapor is generally concentrated nearthe center of the tube, and the liquid is displaced toward the wall ofthe tube. Annular flow is generally characterized as vapor forming acontinuous core down the center of the tube and a liquid film flowingalong the wall of the tube.

To predict existence of a particular flow regime, or a transition fromone flow regime to another, requires the above-mentioned visuallyobserved flow regimes to be quantified in terms of measurable (orcomputed) quantities. This is normally accomplished through the use of aflow regime map. An example of a flow regime map is provided in FIG.59A. The flow regime map shown in FIG. 59A is valid for steam-watersystems and shows ρ_(vapor)*j_(vapor) ² on the x-axis andρ_(vapor)*j_(vapor) ² on the y-axis. A similar flow regime map can becreated for a dielectric coolant 50, such as a hydrofluorocarbon orhydrofluorether, flowing over a heat-generating surface 12 within a heatsink module 100 or flowing within a flexible section of tubing 225, asdescribed herein.

FIG. 59B shows the four two-phase flow regimes, including bubbly flow,slug flow, churn flow, and annular flow, plotted on void fraction versusmass flux axes. To maintain stability within the cooling apparatusduring operation, it can be desirable to maintain single-phase liquidflow, bubbly flow, or a combination thereof throughout the apparatus.Experimental testing confirmed that bubbly flow does not result in flowinstabilities within the cooling apparatus 1. To remain comfortablywithin the bubbly flow regime, it can be desirable to maintain thecoolant below a predetermined void fraction and/or above a predeterminedmass flux. The desired predetermined void fraction and predeterminedmass flux can depend on several factors, including the configuration ofthe cooling apparatus 1 (e.g. components and layout), the type ofcoolant 50 being used, the coolant pressure within the apparatus, andthe temperature of the surface to be cooled 12. In some examples, thevoid fraction of the coolant exiting the heat sink module 100 can beabout 0-0.5, 0-0.4, 0-0.3, 0-0.2, or 0-0.1. In some examples, the massflux of the coolant flowing through a heat sink module 100 can be about10-2,000, 500-1,000, 750-1,500, 1,000-2,500, 2,250-2,500, 2,000-2,700,or greater than 2,700 kg/m2-s. As shown in FIG. 59B, as the voidfraction increases (e.g. from about 0.3-0.5), the mass flux of thecoolant 50 must also increase to avoid transitioning from bubbly flow toslug or churn flow at an outlet of the heat sink module 100 in theflexible tubing 225.

FIG. 60 shows a flow boiling curve where heat transfer rate is plottedas a function of “excess temperature” (T_(e)). Excess temperature is thedifference between the actual temperature of the surface to be cooled 12and the fluid saturation temperature (T_(e)=T_(surface)−T_(sat)). Thecurve is divided into 5 regions (a, b, c, d, and e), each correspondingto certain heat transfer mechanisms.

In region (a) of FIG. 60, a minimum criterion for boiling is that thetemperature of the heat-generating surface 12 exceeds the localsaturation temperature of the coolant (T_(sat)). In other words, somedegree of excess temperature (T_(e)) is required for boiling to occur.In region (a), the excess temperature may be insufficient to supportbubble formation and growth. Therefore, heat transfer may occurprimarily by single-phase convection in region (a).

In region (b) of FIG. 60, bubbles begin forming at nucleation sites onthe heat-generating surface 12. These nucleation sites are generallyassociated with crevices or pits on the heat-generating surface 12 inwhich non-dissolved gas or vapor accumulates and results in bubbleformation. As the bubbles grow and depart from the surface 12, theycarry latent heat away from the surface and produce turbulence andmixing that increases the heat transfer rate. Boiling under theseconditions is referred to as nucleate boiling. In region (b), heattransfer is a complicated mixture of single-phase forced convection andnucleate boiling. This region is often called the mixed boiling or“partial nucleate boiling region.” As the temperature of theheat-generating surface 12 increases, the percentage of surface areathat is subject to nucleate boiling also increases until bubbleformation occupies the entire heat-generating surface 12.

In region (c) of FIG. 60, bubble density increases rapidly as thesurface temperature increases further beyond the saturation temperature(T_(sat)). In this region, heat transfer can be dominated by bubblegrowth and departure from the surface 12. Formation and departure ofthese bubbles 275 can transport large amounts of latent heat away fromthe surface 12 and greatly increase fluid turbulence and mixing in thevicinity of the heat-generating surface 12. As a result, heat transfercan become independent of bulk fluid conditions such as flow velocityand temperature. Heat transfer in this region is know as “fullydeveloped nucleate boiling” and is characterized by a substantialincrease in heat transfer rate in response to only moderate increases insurface 12 temperature. However, there is a limit to the maximum rate ofheat transfer that is attainable with fully developed nucleate boiling.At some point, the bubble density at the heat generating surface 12cannot be increased any further. This point is know as the critical heatflux (“CHF”) and is denoted as c* in FIG. 60. One theory is that atpoint c*, the bubble density becomes so high that the bubbles 275actually impede the flow of liquid back to the surface 12, since bubblesin close proximity tend to coalesce, forming insulating vapor patchesthat effectively block the liquid coolant from reaching theheat-generating surface 12 and thereby prevent the liquid coolant fromextracting latent heat, for example, by undergoing a phase change (i.e.boiling) at the surface 12.

It may be possible to delay the onset of critical heat flux by employingthe cooling apparatuses 1 and methods described herein (e.g. heat sinkmodules capable of providing jet stream 16 impingement) that increasethe heat transfer rate from the heated surface 12, thereby allowing thecooling apparatus 1 to safely and effectively cool a heat generatingsurface 12 that is at a temperature well above the saturationtemperature of the coolant (e.g. about 20-30 degrees C. above T_(sat))without reaching or exceeding critical heat flux. In some examples,delaying the onset of critical heat flux, and thereby increasing theheat transfer rate of the cooling apparatus 1 to previously unattainablerates, can be achieved by increasing the three-phase contact line 58length, as described herein (see e.g. FIG. 63 and related description),by using the methods and components (e.g. heat sink modules 100)described herein, which can provide a plurality of jet stream 16impinging against a heated surface 12 where the jets are positioned at apredetermined jet height 18 away from the heated surface 12. To delaythe onset of critical heat flux (and thereby allow the cooling apparatus1 to operate safely and effectively in region (c) shown in FIG. 60), amass flow rate 51, jet height 18, orifice 155 diameter, coolanttemperature, and coolant pressure can be selected from the rangesdescribed herein to provide a plurality of jet streams 16 that impingethe surface to be cooled 12 and effectively increase the three-phasecontact line 58 length proximate the surface to be cooled 12. Althoughthe cooling apparatus 1 can operate extremely well in regions (a) and(b), the efficiency of the cooling apparatus 1 may be highest whenoperating in region (c).

As the temperature of the surface 12 increases beyond the temperatureassociated with critical heat flux, the heat transfer rate actuallybegins to decrease, as shown in region (d) of FIG. 60. Further increasesin the surface 12 temperature simply result in a higher percentage ofthe surface 12 being covered by insulating vapor patches. Theseinsulating vapor patches reduce the area available for liquid to vaporphase change (i.e. boiling). Therefore, despite the surface temperature(T_(surface)) continuing to increase, the overall heat transfer rateactually decreases, as shown in region (d) of FIG. 60. This region isreferred to as the partial film or “transition film boiling region.”Reaching or exceeding the temperature associated with critical heat fluxcan be undesirable, since performance can decrease and becomeunpredictable. Moreover, due to rapid production of vapor proximate thesurface to be cooled 12, the two-phase flow in the cooling apparatus 1can increase in quality and transition from bubbly flow to slug, churn,or annular flow, which can result in undesirable pressure surges withinthe system due to a volume fraction of vapor exceeding a stable workingrange. It is therefore desirable to operate in regions (a), (b), or (c),below the onset of critical heat flux at point c*. Where the coolingapparatus 1 includes a vapor quality sensor 880 near an outlet port 110of the heat sink module 100, as shown in FIG. 74, the cooling apparatusis capable of operating beyond the onset of critical heat flux at pointc*, and even up to the Leidenfrost point. In this arrangement, the vaporquality sensor 880 provides feedback to an electronic control unit 850that can rapidly control the pressure and flow rate of coolant 50 thoughthe heat sink module 100. For instance, if the vapor quality sensor 880provides a signal to the electronic control unit 850 that is above apredetermined threshold, indicating a vapor quality that is beyond amaximum allowable vapor quality, the electronic control unit caninstruct the pump 20 to increase mass flow rate of coolant through theheat sink module, either by increasing the pressure, velocity, or bothof the flowing coolant. In some examples, the flow quality sensor 880can be an annular shaped sensor that fits over an outer circumference ofthe flexible tubing 225 and provides a signal to the electronic controlunit 850 wirelessly or through a wired connection.

In region (e) of FIG. 60, a vapor layer covers the heat-generatingsurface 12. In this region, heat transfer occurs by conduction andconvection through the vapor layer with evaporation occurring at theinterface between the vapor layer and the liquid coolant. This region isknown as the “stable film boiling region.” Similar to region (d), region(e) is may not be suitable for stable operation of the cooling apparatus1 due to significant vapor formation resulting in slug, churn, orannular flow.

FIG. 61 shows a flow boiling curve for water at 1 atm, where heat fluxis plotted as a function of excess temperature. As noted above, excesstemperature is the difference between the actual temperature of thesurface to be cooled 12 and the fluid saturation temperature(T_(e)=T_(surface)−T_(sat)). The curve of FIG. 61 shows the onset ofnucleate boiling, the point of critical heat flux, and the Leidenfrostpoint. Between the critical heat flux point and the Leidenfrost point isa transition boiling region where the coolant vaporizes almostimmediately on contact with the heated surface 12. The resulting vaporsuspends the liquid coolant on a layer of vapor within the outletchamber 150 and prevents any further direct contact between the liquidcoolant and the heated surface 12. Since vapor coolant has a much lowerthermal conductivity than liquid coolant, further heat transfer betweenthe heated surface 12 and the liquid coolant is slowed downdramatically, as shown by the downward slope of the plot between CHF andthe Leidenfrost point. Beyond the Leidenfrost point, radiation effectsbecome significant, as radiation from the heated surface 12 transfersheat through the vapor layer to the liquid coolant suspended above thevapor layer, and the heat flux again increases.

Coolant

As used herein, the general term “coolant” refers to any fluid capableof undergoing a phase change from liquid to vapor or vice versa at ornear the operating temperatures and pressures of the cooling apparatuses1. The term “coolant” can refer to fluid in liquid phase, vapor phase,or mixtures thereof (e.g. two-phase bubbly flow). A variety of coolants50 can be selected for use in the cooling apparatus 1 based on cost,level of optimization desired, desired operating pressure, boilingpoint, and existing safety regulations that govern installation (e.g.such as regulations set forth in ASHRAE Standard 15 relating topermissible quantities of coolant per volume of occupied buildingspace).

Selection of the coolant 50 for the cooling apparatus 1 can beinfluenced by desired dielectric properties of the coolant, a desiredboiling point of the coolant, and compatibility with polymer materialsused to manufacture the heat sink module 100 and the flexible tubing 225of the apparatus 1. For instance, the coolant 50 may be selected toensure little or no permeability through system components (e.g. heatsink modules 100 and flexible tubing 225) and no damage to any systemcomponents (e.g. to ensure that pump 20 or quick-connect seals are notdamaged or compromised by the coolant 50).

Water is readily abundant and inexpensive. Although the coolingapparatuses 1 described herein can be configured to operate with wateras a coolant, water has certain traits that make it less desirable thanother coolant options. For instance, water does not change phase at alow temperature (such as 40-50° C.) without operating at very lowpressures, which can be difficult to maintain in a relativelyinexpensive cooling apparatus that includes at least some standardfittings and system components (e.g. gear pumps, pressure regulators,valves, and flexible tubing). In addition, water as a coolant requires anumber of additives (e.g. corrosion inhibitors and mold inhibitors) andcan absorb a range of materials from surfaces of system components itcontacts. As water changes phase, these materials can precipitate out ofsolution, causing fouling or other issues within system components.Fouling is undesirable, since it can reduce system performance byeffectively increasing the thermal resistance of certain components thatare tasked with expelling heat from the system (e.g. heat exchanger 40)or tasked with absorbing heat into the system from devices being cooledby the system (e.g. copper base plate 430). The above-mentionedchallenges can be overcome with appropriate filtration and fittings,which adds cost to the system. However, water is a highly effective heattransfer medium, so where increased heat transfer rates are required,and where the risk of failure of the electronic components is acceptableif a leak develops, the additional cost and complexity associated withusing water as the coolant may be justified. But in most practicalsituations, such as cooling servers 400 in data centers, the risk ofloss is not acceptable due to the high cost of servers, so water shouldbe avoided as a coolant.

In some examples, it can be preferable to use a dielectric fluid, suchas a hydrofluorocarbon (HFC) or a hydrofluoroether (HFE) instead ofwater as a coolant 50 in the cooling apparatus 1. Unlike water,dielectric coolants 50 can be used in direct contact with electronicdevices, such as CPUs, memory modules, and power inverters withoutshorting electrical connections of the devices. Therefore, if a leakdevelops in the cooling apparatus and coolant drips onto an electricaldevice, there is no risk of damage to the electrical device. In someexamples of the cooling apparatus 1, the dielectric coolant 50 can bedelivered directly (e.g. by way of one or more jet streams 16) onto oneor more surfaces of the electronic device (e.g. one or more surfaces ofa microprocessor 415), thereby eliminating the need for commonly-usedthermal interface materials (e.g. copper base plates 430 and thermalbonding materials) between the flowing coolant 50 and the electronicdevice and can thereby eliminate thermal resistances associated withthose thermal interface materials, thereby enhancing performance andoverall efficiency of the cooling apparatus 1.

Non-limiting examples of dielectric coolants 50 include1,1,1,3,3-pentafluoropropane (known as R-245fa), hydrofluoroether (HFE),1-methoxyheptafluoropropane (known as HFE-7000),methoxy-nonafluorobutane (known as HFE-7100). One version of R-245fa iscommercially available as GENETRON 245fa from Honeywell InternationalInc. headquartered in Morristown, N.J. HFE-7000 and HFE-7100 (as well asHFE-7200, HFE-7300, HFE-7500, HFE-7500, and HFE-7600) are commerciallyavailable as NOVEC Engineered Fluids from 3M Company headquartered inMapleton, Minn. FC-40, FC-43, FC-72, FC-84, FC-770, FC-3283, and FC-3284are commercially available as FLUOROINERT Electronic Liquids also from3M Company.

GENETRON 245fa is a pentafluoropropane and has a boiling point of 58.8degrees F. (˜14.9 degrees C.) at 1 atm, a molecular weight of 134.0, acritical temperature of 309.3 degrees F., a critical pressure of 529.5psia, a saturated liquid density of 82.7 lb/ft3 at 86 degrees F., aspecific heat of liquid of 0.32 Btu/lb-deg F at 86 degrees F., and aspecific heat of vapor of 0.22 btu/lb-deg F at 1 atm and 86 degrees F.GENETRON 245fa has a Safety Group Classification of A1 under ANSI/ASHRAEStandard 36-1992. For cooling a processor 415 that has a preferredoperating core temperature of about 60-70 degrees C., GENETRON 245fa canbe provided at a pressure greater than atmospheric pressure to increaseits saturation temperature to about 25-35, 30-40, or 35-50 degrees C. toensure the bulk of the coolant remains in liquid phase at it passesthrough the heat sink module 100. For flow rates of about 0.25-1.25liters per minute of subcooled GENETRON 245fa through the heat sinkmodule 100, the rate of boiling can depend on the processor utilizationlevel. For instance, when the processor 415 is idling, the subcooledGENETRON 245fa may experience no local boiling, and when the processoris fully utilized, the subcooled GENETRON 245fa may experience vigorouslocal boiling and bubble 275 generation.

NOVEC 7000 has a boiling point of 34 degrees C., a molecular weight of200 g/mol, a critical temperature of 165 degrees C., a critical pressureof 2.48 MPa, a vapor pressure of 65 kPa, a heat of vaporization of 142kJ/kg, a liquid density of 1400 kg/m3, a specific heat of 1300 J/kg-K, athermal conductivity of 0.075 W/m-K, and a dielectric strength of about40 kV for a 0.1 inch gap. For cooling a processor 415 that has apreferred operating core temperature of about 60-70 degrees C., NOVEC7000 works well. For flow rates of about 0.25-1.25 liters per minute ofsubcooled NOVEC 7000 through the cooling line, where the subcooled NOVEC7000 is delivered to the heat sink module 100 at a pressure of about 15psi and a temperature of about 25 degrees C., local boiling of thecoolant may occur proximate the surface to be cooled. The rate ofboiling can depend on the processor utilization level. For instance,when the processor is idling, the NOVEC 7000 may experience no localboiling, and when the processor is fully utilized, the NOVEC mayexperience vigorous local boiling and bubble 275 generation.

NOVEC 7100 has a boiling point of 61 degrees C., a molecular weight of250 g/mol, a critical temperature of 195 degrees C., a critical pressureof 2.23 MPa, a vapor pressure of 27 kPa, a heat of vaporization of 112kJ/kg, a liquid density of 1510 kg/m3, a specific heat of 1183 J/kg-K, athermal conductivity of 0.069 W/m-K, and a dielectric strength of about40 kV for a 0.1 inch gap. NOVEC 7100 works well for certain electronicdevices, such as power electronic devices that produce high heat loadsand can operate safely at temperatures above about 80 degrees C.

NOVEC 649 Engineered Fluid is also available from 3M Company. It is afluoroketone fluid (C₆-fluoroketone) with a low Global Warming Potential(GWP). It has a boiling point of 49 degrees C., a thermal conductivityof 0.059, a molecular weight of 316 g/mol, a critical temperature of 169degrees C., a critical pressure of 1.88 MPa, a vapor pressure of 40 kPa,a heat of vaporization of 88 kJ/kg, a liquid density of 1600 kg/m3.

In some examples, the coolant 50 can be a combination of dielectricfluids described above. For instance, the coolant 50 can include acombination of R-245fa and HFE-7000 or a combination of R-245fa andHFE-7100. In one example, the coolant 50 can include about 1-5, 1-10,5-20, 10-20, 15-30, or 25-50 percent R-245fa by volume with theremainder being HFE-7000. In another example, the coolant 50 can includeabout 1-5, 1-10, 5-20, 10-20, 15-30, or 25-50 percent R-245fa by volumewith the remainder being HFE-7100.

Combining two or more types of dielectric fluids to form a coolantmixture for use in the cooling apparatus 1 can be desirable for severalreasons. First, certain fluids, such a R-245fa may be regulated in waysthat restrict the volume of fluid that can be used in an occupiedbuilding, such as an office building. Since R-245fa has been shown toperform well in the cooling apparatus 1, it may be desirable to use asmuch R-245fa as legally permitted in the cooling apparatus 1, and ifadditional coolant volume is required, to use an unregulated coolant,such as HFE-7000 or HFE-7100, to increase the total coolant volumewithin the cooling apparatus 1 to reach a desired coolant volume.

Second, combining dielectric coolants can allow a coolant mixture with adesired boiling point to be formulated. R-245fa has a boiling point ofabout 15 degrees C. at 1 atm, and HFE-7000 has a boiling point of about34 degrees C. at 1 atm. In some examples, neither of these boilingpoints may be optimal for use in a particular application. By combiningR-245fa and HFE-7000, a coolant mixture can be created that behaves asif its boiling point were somewhere between 15 and 34 degrees C.,depending on the mixture ratio. The ability to create a coolant mixturewith a specific boiling point can be highly desirable for customtailoring the coolant mixture for a specific application depending on adesired operating temperature of the surface to be cooled 12.

Cooling Apparatus

FIG. 1 shows a front perspective view of a cooling apparatus 1 installedon a plurality of racks 410 of servers 400 in a data center or computerroom 425. The racks 410 of servers 400 are arranged in a row with a pump20, reservoir 200, and other system components arranged near the leftside of the row of racks 410. One or more tubes extend along the lengthof the row of racks 410 and fluidly connect servers 400 within each rack410 to the cooling apparatus 1, thereby allowing heat-generatingcomponents 12 (e.g. processors) within each server to be cooled by thecooling apparatus 1.

In addition to cooling microprocessors in servers, the cooling apparatuscan be configured to cool a wide variety of other devices. In someexamples, the cooling apparatus 1 can be configured to cool one or moreheat-producing surfaces 12 associated with batteries, electric motors,control systems, power electronics, chemistry equipment (e.g. rotaryevaporators or reflux distillation condensers), or machines ormechanical devices (e.g. turbines, internal combustion engines,radiators, braking components, turbochargers, engine intake manifolds,plasma cutters, drills, oil and gas exploratory and recovery equipment,water jet cutters, welding systems, or computer numerical control (CNC)mills or lathes).

FIG. 2A shows a rear view of the cooling apparatus 1, and FIG. 2B showsa detailed rear view of a right portion of the cooling apparatus shownin FIG. 2A. In this example, the cooling apparatus 1 can include aplurality of components and sub-assemblies fluidly connected to providea cooling apparatus 1 that is capable of locally cooling one or moreheat-producing surfaces 12 (e.g. flat surfaces, curved surfaces, orcomplex surfaces), such as surfaces associated with CPUs, memorymodules, and motherboards located within the server housings.

FIG. 3 shows a left side view of the cooling apparatus 1 of FIG. 1.Portions of a primary cooling loop 300 are visible in FIG. 3, includinga pump 20, reservoir 200, drain/fill location 245, shut-off valve 250,pressure gauge 255, inlet manifold 210, and return line 230. Portions ofa first bypass 305 are also visible in FIG. 3, including a pressureregulator 60 and heat exchanger 40. As shown in FIG. 3, the primarycooling loop 300 and the first bypass 305 can be fluidly connected tothe reservoir 200.

FIGS. 92-95 show a cooling apparatus 1 with redundant pumps (20-1,20-2), shut-off valves 250, a tubular reservoir 200, and a first bypass305. The first bypass 305 can include a pressure regulator 60 and a heatexchanger 40, as shown in FIG. 93. The heat exchanger 40 can include twoindependent fluid pathways, as shown in FIG. 97. A first independentfluid pathway can transport a first bypass flow 51-1 of coolant 50, anda second independent fluid pathway can transport a flow 42 of externalcooling fluid, such as a water-glycol mixture from an external heatrejection loop 43. The coolant 50 in the first independent pathway canbe at a higher temperature than the external cooling fluid in the secondindependent pathway. Heat transfer from the coolant 50 to the externalcooling fluid can cause a decrease in the coolant temperature and anincrease in the external cooling fluid temperature. The external heatrejection loop 43 can reject heat absorbed from the coolant 50 to alocation outside of the data center 425 or distributed computingfacility where the cooling apparatus 1 is located.

As shown in FIGS. 92-95, the fluid distribution unit 10 of the coolingapparatus 1 can be mounted on a moveable stand 49 that allows the unitto be easily moved in a data center 425 when, for example, the layout ofthe data center changes to accommodate an increase or a decrease in thenumber of server racks 410. The fluid distribution unit can include thepump or pumps 20, reservoir 200, and heat exchanger 40. The moveablestand 49 of the fluid distribution unit 10 can have a width and a depthsimilar to a server rack 410, thereby allowing the moveable stand 49 tofit in any area suitable for a server rack. For example, the moveablestand 49 can have a width of about 20-36 inches and a depth of about35-45 inches.

In some data centers, it can be desirable to minimize noise from coolingsystems so that employees do not have to wear hearing protection. In thecooling apparatus 1 described herein, the pump 20 is the only componentof the cooling apparatus that produces noise. In some instances, it maybe desirable to place the fluid distribution unit 10 in a separate roomto isolate pump noise from the data center floor where the racks 410 ofservers 400 are located. The fluid distribution unit 10 can be locatedup to 50 feet away from servers it is actively cooling, so locating thefluid distribution unit in a separate room is feasible. Where a datacenter has a large number of servers that requires multiple coolingapparatuses to provide cooling, the fluid distribution units 10 for allof the cooling apparatuses may be located in the same room or gallery toisolate pump noise.

FIGS. 11A-14, 16-20, 68-72, and 75-83 present a variety ofconfigurations for the cooling apparatus 1. Depending on itsconfiguration, the cooling apparatus 1 can include a plurality offluidly connected components, including one or more pumps 20, one ormore reservoirs 200, one or more heat exchangers 40, one or more inletmanifolds 205, one or more outlet manifolds 210, one or more pressureregulators 60, one or more sections of flexible tubing 225, and one ormore heat sink modules 100 mounted on, or placed in thermalcommunication with, one or more surfaces to be cooled 12.

FIG. 11A shows an exemplary schematic of a cooling apparatus 1 havingone heat sink module 100 mounted on a heat generating surface 12. Theheat-generating surface 12 can be any surface having a temperature aboveambient temperature that requires cooling. For instance, theheat-generating surface 12 can be a surface of a mechanical orelectrical device, such as a surface of a processor 415, such as a CPUor GPU. As identified by dashed lines in FIG. 11B, the cooling apparatus1 can include a primary cooling loop 300 fluidly connecting a pump 20,at least one heat sink module 100, a return line 230, and a reservoir200. The pump 20 can be configured to draw single-phase liquid coolantfrom the reservoir 200 and deliver a flow 51 of pressurized single-phaseliquid coolant 50 to an inlet port 105 of a heat sink module 100. Theheat sink module 100, being mounted on the heat-generating surface 12,can be configured to direct a flow of pressurized coolant 51 at thesurface of the heat-generating surface 12 in the form of a plurality ofjet streams 16 of coolant impinging the heat-generating surface 12,thereby facilitating heat transfer from the heat-generating surface tothe flow of coolant. The return line 230 can be configured to transportthe flow of coolant 51, which may include two-phase bubbly flow, fromthe outlet port 110 of the heat sink module 100 back to the reservoir200 where it can be mixed with single-phase liquid coolant to promotecondensation of vapor bubbles within the two-phase bubbly flow, therebyresulting in transition of the two-phase bubbly flow back tosingle-phase liquid coolant that can once again be delivered to the pump20 without risk of cavitation or vapor lock. FIG. 81 shows a preferredvariation of the schematic shown in FIG. 11A, where single-phase andtwo-phase flow are visually represented in sections of tubing fluidlyconnecting components of the system. Specifically, two-phase bubbly flowis shown exiting an outlet port 110 of the heat sink module 100. FIG. 81also includes an external heat rejection loop that is fluidly connectedto an external dry cooler 40-2, which can be placed outside of the datacenter 425 or on a roof of the data center, thereby allowing heat fromthe cooling apparatus 1 to be rejected outside of the data center andavoiding heating air within the data center.

As identified by dashed lines in FIG. 11C, the cooling apparatus 1 caninclude a first bypass 305 including a pressure regulator 60 and a heatexchanger 40. The purpose of the first bypass 305 can be to divert aportion of the flow 51 away from the primary cooling loop 300 andthrough the heat exchanger 40 where the fluid can be further subcooledand returned to the reservoir 200 to assist in condensing vapor in thereservoir by further reducing the bulk fluid temperature of the liquidcoolant in the reservoir 200. As a result, when the two-phase bubblyflow is delivered to the reservoir via the return line 230, itimmediately mixes in the reservoir 200 with a large volume of coolant 50that is well below the saturation temperature of the liquid, therebypromoting condensing of all vapor bubbles entering the reservoir via thereturn line. The portion of flow 51 that is diverted through the firstbypass 305 can be controlled, at least in part, by adjusting thepressure regulator 60 located in the first bypass 305. The preferredamount of flow 51-1 that is diverted through the first bypass 305 maydepend on the reservoir temperature and/or the quality (x) of the flowreturning to the reservoir via the return line 230. For example, if thetemperature of the fluid in the reservoir 200 reaches a predeterminedthreshold value (e.g. if the temperature of the coolant in the reservoirincreases to about 10-15 degrees below the saturation temperature of thecoolant), or if the quality of the flow in the return line 230 reaches apredetermined threshold value (e.g. if the quality of the flow in thereturn line 230 reaches a value of about 0.25-0.35, 0.3-0.4, 0.35-0.5),it can be desirable to increase the amount of flow through the firstbypass 305 to reject heat from the coolant using the heat exchanger sothat cool liquid coolant can be circulated back to the reservoir 200 toensure that vapor bubbles 275 entering via the return line 230 rapidlycondense within the reservoir 200 and are not permitted to reach thepump 20. Through this approach, a supply of single-phase liquid coolantcan be provided from the reservoir 200 to the pump to ensure stable pumpoperation.

In the schematic shown in FIG. 11A, the heat exchanger 40 is positioneddownstream of the pressure regulator 60, but this is not limiting. Inother examples, the pressure regulator 60 can be positioned downstreamof the heat exchanger 40, as shown in FIG. 12A, where the coolingapparatus 1 has one heat sink module 100 mounted on a heat source 12 anda pressure regulator 60 located downstream of the heat exchanger 40 inthe first bypass 305.

As identified by dashed lines in FIG. 11D, the cooling apparatus 1 caninclude a second bypass 310 including a pressure regulator 60. Thesecond bypass 310 can route a portion of the pressurized single-phaseliquid flow around the heat sink module 100 and can be fluidly connectto the primary cooling loop 300 downstream of the heat sink module 100.Depending on the surface temperature of the heat-generating surface 12and settings of the cooling apparatus (e.g. pressure, flow rate, coolanttype, bulk coolant temperature at the module inlet 105, coolantsaturation temperature, etc.), the primary cooling loop 300 may betransporting two-phase bubbly flow downstream of the outlet port 110 ofthe heat sink module 100. To encourage condensing of bubbles 275 withinthe two-phase bubbly flow before the coolant reaches the reservoir (andthereby reducing the likelihood of vapor being introduced to the pump20), the second bypass 310 can route single-phase liquid coolant aroundthe heat sink module 100 and deliver the single-phase liquid coolant tothe primary cooling loop 300 that is carrying two-phase bubbly flow,effectively mixing the two flows upstream of the reservoir 200. Thismixing encourages condensing of all or a portion of the bubbles in thetwo-phase bubbly flow before the flow is delivered back to the reservoir200 via the return line 230, thereby further reducing the likelihoodthat any bubbles 275 will be drawn from the reservoir 200 and fed to thepump, where they could cause unwanted cavitation.

Because the bubbles 275 formed in the two-phase bubbly flow arerelatively small and are distributed (i.e. dispersed) throughout theliquid coolant 50, the bubbles are carried through the primary coolingloop 300 by the momentum of the liquid coolant and do not travelvertically within the system due to gravitational effects. Consequently,the cooling apparatus 1 does not require a condenser mounted at a highpoint in the system to collect and condense vapor bubbles back toliquid, as competing systems do. Since no condenser is required, thecooling apparatus 1 can be much smaller in size and less expensive thancompeting systems that require a condenser. Also, the heat sink modules100 and sections of flexible tubing 225 described herein can beinstalled in any orientation without concerns of vapor lock. To thecontrary, in competing systems, the orientation of system components canbe critical to ensure that all vapor is transported to a condenserlocated at a high point in the system by way of gravity to ensure thatvapor does not make its way to the pump, where it could result in vaporlock and/or pump cavitation and system failure.

As used herein, “fluid communication” between two or more elementsrefers to a configuration in which fluid can be communicated between oramong the elements and does not preclude the possibility of having afilter, flow meter, temperature or pressure sensor, or other devicesdisposed between such elements. The elements of the cooling apparatus 1are preferably configured in a closed fluidic system, as shown in FIG.11A, thereby permitting containment of the coolant 50 which couldotherwise evaporate into the environment.

Pressure Regulator

The pressure regulator 60 can be any suitable type of pressure regulatorthat is capable of achieving suitable working pressure ranges and flowrates described herein to ensure smooth operation of the coolingapparatus 1. In some examples, the pressure regulator 60 can be a reliefvalve, such as a Series 69 relief valve manufactured by Aquatrol, Inc.of Elburn, Ill. One suitable Series 69 relief valve has an adjustmentrange of about 0-15 psi and a maximum flow rate of about 6.9 gallons perminute. This model pressure regulator is suitable for a coolingapparatus 1 configured to cool several racks 410 of servers 400 as shownin FIG. 3. For applications where a larger or smaller cooling apparatus1 is required, a larger or smaller pressure regulator can be selected.

The pressure regulator 60 can be a differential pressure bypass valve.In one example, the pressure regulator 60 can be a 519 Seriesdifferential pressure bypass valve from Caleffi S.p.a of Italy. The 519series valve can provide a differential pressure of about 2-10, 5-12, or10-15 psi between an inlet and an outlet of the valve 60. A model of the519 Series valve with a 0.75-inch diameter can flow up to 9 gpm, a modelwith a 1-inch diameter can flow up to 40 gpm, and a model with a1.25-inch diameter can flow up to 45 gpm. The size of the pressureregulator 60 can be selected based on a desired flow rate, which candepend on the number of cooling lines 303 present in the coolingapparatus 1.

As shown in FIGS. 11A and 11D, the pressure regulator 60 can be locatedin the second bypass 310 of the cooling apparatus 1 and can be used tocontrol the pressure differential between the inlet port 105 and theoutlet port 110 of the heat sink module (i.e. the pressure differentialbetween the high-pressure coolant 54 at the inlet port 105 and thelow-pressure coolant 55 at the outlet port 110). By doing so, thepressure regulator can be used to adjust the flow rate through the heatsink module 100. Where the cooling apparatus 1 has a plurality of heatsink modules 100 fluidly connected in parallel to the inlet manifold 210and outlet manifold 215, as shown in FIG. 16, the pressure regulator 60in the second bypass can be used to control the pressure differentialbetween the inlet manifold 210 and the outlet manifold 215, and therebycontrol flow through the heat sink modules 100.

In the cooling apparatus 1 shown in FIG. 11A, by adjusting the pressureregulator 60 located in the second bypass 310, the pressure differentialbetween the inlet port 105 and outlet port 110 can be controlled. In thecooling apparatus 1 shown in FIG. 16, the pressure regulator 60 can beadjusted to provide a pressure differential between the inlet manifold210 and the outlet manifold 215. In one example, the pressure regulator60 can be adjusted to provide a pressure differential of about 5-15 or10-15 psi between the inlet manifold 210 and the outlet manifold 215.For instance, if the high-pressure coolant 54 in the inlet manifold 210is at a pressure of about 60 psi, the pressure regulator 60 can beadjusted to maintain low-pressure coolant 55 in the outlet manifold 215at a pressure of about 45-55 or 45-50 psi. In another example, if thehigh-pressure coolant 54 in the inlet manifold 210 is at a pressure ofabout 30 psi, the pressure regulator 60 can be adjusted to maintainlow-pressure coolant 55 in the outlet manifold 215 at a pressure ofabout 15-25 or 15-20 psi. In yet another example (where the contents ofthe cooling apparatus 1 are evacuated using a vacuum pump prior toadding the coolant, such that the resting pressure of the coolant isnear or below atmospheric pressure), if the high-pressure coolant 54 inthe inlet manifold 210 is at a pressure of about 15 psi, the pressureregulator 60 can be adjusted to maintain low-pressure coolant 55 in theoutlet manifold 215 at a pressure of about 0-10 or 0-5 psi.

The pressure regulator 60 located in the second bypass 310 of thecooling apparatus 1, as shown in FIG. 16, can be adjusted to control thecoolant flow rate through the second bypass 310, and by doing so, cansimultaneously adjust the coolant flow rate through the heat sinkmodules 100. For instance, as the pressure differential between theinlet manifold 210 and the outlet manifold 215 shown in FIG. 16 isdecreased by adjusting the pressure regulator 60 located in the secondbypass 310, a higher percentage of coolant flow 51 will pass through thepressure regulator 60, effectively bypassing the heat sink modules 100and resulting in a reduced coolant flow rate through the heat sinkmodules. Conversely, as the pressure differential between the inletmanifold 210 and outlet manifold 215 is increased by adjusting thepressure regulator 60 located in the second bypass 310, a lowerpercentage of coolant flow 51 will pass through the pressure regulator60, resulting in an increased coolant flow rate through the heat sinkmodules 100.

As shown in FIG. 16, the pressure regulator 60 can be arranged inparallel with a plurality of cooling lines extending between the inletand outlet manifolds (210, 215). Coolant flow through the pressureregulator 60 and the cooling lines can be similar to the way currentflows in a circuit with resistors arranged in parallel. Increasing theflow resistance of the regulator 60 will decrease the flow through thesecond bypass 310 and increase the flow rate through the cooling lines.Conversely, decreasing the flow resistance of the regulator 60 willincrease the flow through the second bypass 310 and decrease the flowrate through the cooling lines. Similarly, increasing the flowresistance of the regulator 60 in the first bypass will decrease theflow rate through the heat exchanger 40, and decreasing the flowresistance of the regulator 60 in the first bypass will increase theflow rate through the heat exchanger 40.

Flow Control Based on Two-Phase Flow Sensor

In some examples, the quality (x) of the two-phase bubbly flow exitingthe heat sink module(s) 100 can be monitored with a sensor 880, and anoutput signal from the sensor can be input to an electronic control unit850 capable of changing one or more operating conditions of the coolingapparatus 1. For instance, when the flow quality (x) exiting the heatsink module 100 reaches a predetermined threshold value (e.g. about0.25, 0.3, 0.35, or 0.4), the flow resistance of the pressure regulator60 in the second bypass 310 can be increased to reduce the flow ratethrough the pressure regulator and increase the flow rate through theheat sink module(s) 100, thereby reducing the quality (x) of the flowexiting the heat sink module(s) to ensure the bubbly-flow does nottransition to slug flow or churn flow (see FIG. 59B) within the flexibletubing 225, which could result in flow instabilities.

In another example, when the flow quality (x) exiting the heat sinkmodule 100 reaches a predetermined threshold value, the pump 20 speedcan be increased to increase the mass flow rate of coolant 50 (e.g. byincreasing coolant pressure, velocity, or both) through the coolingline(s) 303 and heat sink module(s) 100, thereby reducing the quality(x) of the flow exiting the heat sink module(s) to ensure the two-phasebubbly-flow does not transition to slug flow or churn flow (see FIG.59B) within the flexible tubing 225, which could result in flowinstabilities. The coo

The flow sensor 880 can be any suitable senor capable of detecting flowquality, flow patterns, or void fraction identification. The sensor canemploy high-speed photography, x-ray, or other suitable imagingtechniques. In some examples, the sensor 880 can employ ultrasonicsensing. The sensor 880 can include one ultrasonic sensor or an array ofultrasonic sensors. The sensor 880 can include integrated signalconditioning software. The sensor 880 can be noninvasive to the coolinglines 303. The output from the flow sensor 880 can be delivered as inputto the electronic control unit 850 wirelessly or through a wiredconnection. In some examples, the electronic control unit 850 can beconnected to an intranet system, thereby allowing the output from theflow sensor to be viewed on a remote terminal, such as a computer in anadjacent office building. The output signal of the flow sensor can bestored on a computer readable medium, and the output versus time can beanalyzed against CPU utilization to identify unexpected variations inflow quality that may predict when maintenance of the cooling apparatus,such as maintenance of pump seals, is required.

Pump

The pump 20 can be any pump capable of generating a positive coolantpressure that forces coolant 50 to circulate through the coolingapparatus 1. In some examples, the pump 20 can generate a positivecoolant pressure that forces coolant through the primary cooling loop300, into an inlet port of a heat sink module 100, and through aplurality of orifices 155 within the heat sink module, therebytransforming the flow of coolant into a plurality of jet streams 16 ofcoolant that impinge against the surface to be cooled 12, as shown inFIG. 26. In some examples, it can be desirable to select a pump 20 thatis capable of pumping single-phase liquid coolant and increasing thepressure of the coolant to about 5-20, 15-30, 25-45, 30-50 40-65, 50-75,60-85, 75-150, 5-200, 5-150, or 100-200 psi. Lower pressures can bedesirable for reducing power consumption by the pump and therebyincreasing overall efficiency of the cooling apparatus 1. A desiredcoolant pressure can depend on the type of coolant selected, the boilingpoint of that coolant, and the temperatures of the one or more surfacesto be cooled 12.

To allow the cooling apparatus 1 to operate at a relatively low pumpoutlet pressure, and thereby consume minimal power and allow for the useof lightweight, inexpensive, flexible tubing 225, it can be desirable toselect a coolant 50 that has a boiling point that is a predeterminednumber of degrees below the temperature of the surface to be cooled 12at the system operating pressure. In some examples, a coolant 50 with aboiling point about 10-20, 15-25, 20-30, 25-35, 30-45, 40-60, or 50-75degrees C. below the temperature of the surface to be cooled 12 can beselected, where the boiling point of the coolant is determined at apressure coinciding with an inlet pressure at the heat sink module 100.Experiments show that providing coolant to a first heat sink module 100at about 10-20 degrees C. below the temperature of the surface to becooled 12 provides effective cooling and formation of bubbly flow insubsequent series-connected heat sink modules 100.

When adapting the cooling apparatus 1 to cool microprocessors 415 thatoperate with junction temperatures of about 50-90 degrees C., it can bedesirable to select a dielectric coolant such as HFE-7000 that has aboiling point of about 34 degrees C. at 1 atm. In this arrangement, thepump outlet pressure can be set to about 5-35 or 15-25 psia to achievesuitable operation, and the pressure regulator 60 in the first bypass305 can be adjusted to divert about 30-60% of the flow 51 from the pumpoutlet 22 through the first bypass 305 and through the heat exchanger 40to ensure a volume of adequately subcooled coolant in the reservoir 200.In FIG. 75, this first bypass flow is identified as 51-1. When adaptingthe cooling apparatus 1 to cool power electronic devices that operate attemperatures of about 90-120 degrees C., it can be desirable to select adielectric coolant with a higher boiling point, such as HFE-7100 thathas boiling point of about 61 degrees C. at 1 atm. When adapting thecooling apparatus 1 to cool an electrical device having a temperature ofabout 45-100 degrees C., it can be desirable to select a dielectriccoolant such as HFE-7000 that has a boiling point of about 34 degrees C.at 1 atm or R-245 fa that has a boiling point of about 15 degrees C. at1 atm.

The pump outlet pressure and pressure regulators 60 can be adjusted toprovide a suitable flow of coolant though the heat sink module 100whereby a portion of the liquid coolant changes to vapor and a portionof the coolant remains liquid to produce a two-phase bubbly flow havinga quality below a predetermined threshold to ensure stable flow withinthe cooling apparatus 1.

In some examples, the contents of the cooling apparatus 1 can beevacuated using a vacuum pump prior to adding the coolant 50, therebyresulting in a sub-atmospheric pressure within the cooling apparatus 1.The coolant can then be added to the system from a container that hasbeen degassed and is also at a sub-atmospheric pressure. Once inside thesystem, the coolant will remain at a sub-atmospheric pressure. When thepump 20 is activated, it pumps single-phase liquid coolant and increasesthe pressure of the coolant to about 5-20, 10-25, or 15-30 psi at thepump outlet 22. In this example, the coolant 50 can be HFE-7000, and thepump pressure can be set at a suitable value to provide a flow rate ofabout 0.25-1.75, 0.7-1.3, 0.8-1.2, or 0.9-1.1 liters per minute or about1.0 liter per minute through each heat sink module 100 in the coolingapparatus 1.

In other examples, the coolant can be HFE-7000, HFE-7100, R-245fa, or amixture thereof. In some examples, the coolant can be 100% HFE-7000,100% HFE-7100, or about 60-95, 70-95, or 85-95% HFE-7000 by volume andthe remainder can include R-245fa. In any of these examples, the pumppressure can be set at a suitable value to provide a flow rate of about0.25-1.75, 0.7-1.3, 0.8-1.2, or 0.9-1.1 liters per minute through eachheat sink module 100 in the cooling apparatus 1. Where multiple (i.e.two or more) heat sink modules 100 are connected in series along acooling line 303, the pump pressure can be set a suitable value toprovide a flow rate of about 0.25-1.75, 0.7-1.3, 0.8-1.2, or 0.9-1.1liters per minute through the cooling line 303 in the cooling apparatus1.

In one example, the pump 20 can be a variable speed positivedisplacement pump, such as a MICROPUMP gear pump by Cole-Parmer ofVernon Hills, Ill. In another example, where the cooling apparatus 1 isconfigured to cool several racks 410 of servers 400, as shown in FIGS.1-3, the pump 20 can be a 1.5 HP vertical, multistage, in-line,centrifugal pump, such as Model No. A96084444P115030745 from Grundfosheadquartered in Denmark. In a redundant configuration, as shown inFIGS. 9 and 10, the redundant cooling apparatus 2 can have two Grundfospumps 20 operating simultaneously or with one pump operating and anautomatic failover circuit that activates the second pump if the firstpump fails. FIG. 96 shows an exploded view of a horizontal, in-line,centrifugal pump 20 with a first shut-off valve 250 located near a pumpinlet 21 and a second shut-off valve 250 located near a pump outlet 22.

In one configuration shown in FIGS. 92-95, the cooling apparatus 1 canhave two parallel redundant pumps (20-1, 20-2) that supply pressurizedcoolant to a common cooling apparatus 1. In this configuration, eachpump 20 can be sized to independently provide an adequate flow 51 ofpressurized coolant 50 to the cooling apparatus 1, thereby requiringoperation of only one pump at a time, while the other pump remains onstandby. The cooling apparatus 1 can include a failover circuit that, incase of failure of a first pump 20-1, automatically detects the failureand activates a second pump 20-2 to provide a nearly uninterrupted flow51 of pressurized coolant 50 through the system 1. In one example, pumpfailure can be detected by monitoring a signal from a pressure sensor880 mounted at a sensor mounting location 875 near a pump outlet 22 andidentifying a failure when the signal decreases below a predeterminedlower threshold value. For instance, if the pressure decreases more than20 percent below a target value, the microcontroller 850 may identify apump failure, deactivate the first pump 20-1, and activate the secondpump 20-2. Deactivating the first pump 20-1 can include commandingshut-off valves 250 at in inlet and an outlet of the first pump toclose, and activating the second pump 20-2 can include commandingshut-off valves 250 at an inlet and an outlet of the second pump toopen. Closing shut-off valves 250 associated with the first pump 20-1can minimize flow restrictions in the primary cooling loop 300 andthereby reduce pumping losses and improve system efficiency.

Although a constant speed pump 20 can be used for simplicity, a variablespeed pump (e.g. with a variable frequency drive) can provide greaterflexibility for cooling dynamic heat loads, such as microprocessors 415with varying utilization rates and temperatures, since the variablespeed pump can enable the flow 51 of coolant 50 to be adjusted to meet aflow rate required to cool the estimated (e.g. theoretical) or actual(e.g. measured) heat load at the one or more surfaces to be cooled 12,and then adjusted in real-time if the heat load is greater or less thanthe estimated heat load. More specifically, increasing the flow rate ofcoolant 50 may be required where the heat load is greater than theestimated heat load to avoid reaching critical heat flux at the surfaceto be cooled 12. Alternately, decreasing the flow rate of coolant 50 maybe required where the heat load is less than the estimated heat load toreduce unnecessary power consumption by the pump 20. The variable speedpump can be controlled by an electronic control system of the coolingapparatus 1.

A variable speed pump can also be used to automatically adjust pumpspeed to compensate for changes in the number of servers 400 connectedto the cooling apparatus 1. For instance, where quick-connect fittingsare provided on the inlet and outlet manifolds, a service technician mayneed to connect or disconnect several servers 400 (or an entire rack 410of servers) from the cooling apparatus 1 without the facilityexperiencing downtime. In these instances, the servers 400 can be addedor removed without requiring the service technician to make anyadjustments to the pump pressure. In many data center facilities, aclear division exists between information technology (IT) departmentsand facilities departments. Servers are maintained by the IT department,and mechanical systems, such as pumps 20, are maintained by thefacilities department. Allowing the IT department to add and removeservers without requiring assistance from the facilities department isdesirable and saves both departments time. Therefore, having a variablespeed drive on the pump 20 is desirable, since it allows the coolingapparatus 1 to automatically adjust the pump outlet pressure toaccommodate a change to the number of servers. This allows an ITprofessional to change the number of servers without requiring afacilities professional to adjust the pump or regulator settingsimmediately thereafter.

In some examples, a pressurizer can be used in place of or in additionto the pump 20. The pressurizer can be pressurized by any suitablemethod or device, such as a pneumatic or hydraulic device that covertsmechanical motion to fluid pressure to provide a volume of pressurizedcoolant within the pressurizer that is then used to circulate coolant 50through the cooling apparatus 1.

Reservoir

In the cooling system 1, the pump 20 can be in fluid communication witha coolant reservoir 200. In some examples, the reservoir 200 can be ametal tank, such as a steel or aluminum tank (see, e.g. FIG. 3), or aplastic tank with a suitable pressure rating and made of a polymer thatis compatible with the coolant 50. In other examples, the reservoir 200can be any suitable vessel that is capable of receiving a volume ofcoolant and safely housing the volume of coolant in compliance withgoverning regulations. For instance, as shown in FIGS. 92-95, thereservoir 200 can be a section of pipe having a suitable interior volumeto hold an adequate supply of coolant, where the interior volume of thepipe is defined by a length and inner diameter of the pipe. Thereservoir 200 shown in FIGS. 92-95 can have an inner diameter of about1.5-3.0 inches inches and a length of about 4-6 feet. In some examples,it can be desirable for the reservoir 200 to have an interior volumecapable of holding at least 15, 20, or 25 percent of the total volume ofcoolant in the cooling apparatus 1. The reservoir 200 can supplysubcooled liquid coolant to the pump 20 for stable pump operation. Thereservoir 200 can be located above the pump 20, as shown in FIGS. 92-95,to provide adequate head pressure to ensure a continuous supply ofcoolant 50 from the reservoir 200 to the pump inlet 21.

As described herein, with respect to certain embodiments of the coolingapparatus 1, such as embodiments shown in FIGS. 11A-D, the reservoir 200can be configured to receive a variety of fluid flows, includingtwo-phase bubbly flow via a primary cooling loop 300 and single-phaseliquid flow via a first bypass loop 305. However, despite receivingtwo-phase bubbly flow via the return line 230 of the primary coolingloop 300, the cooling apparatus 1 can be configured to provideexclusively single-phase liquid coolant from a reservoir outlet to aninlet 21 of the pump 20. As vapor bubbles 275 are introduced to thereservoir by bubbly flow from the return line 230, the bubbles 275 tendto migrate to the top of the reservoir 200, and single-phase liquidtends to settle in the lower portion of the reservoir due togravitational effects. A section of tubing 220, such as rigid orflexible section of tubing, can connect the reservoir 200 to the inlet21 of the pump 20. In some examples, the section of tubing 220 canconnect to a reservoir outlet located along a lower portion of thereservoir 200, and preferably at or near a bottom portion of thereservoir, to ensure that only single-phase liquid coolant, and nottwo-phase coolant, is drawn from the reservoir and provided to the inlet21 of the pump 22. Providing only single-phase liquid coolant to thepump 20 can ensure that cavitation within the pump is avoided.Cavitation can occur if two-phase flow is provided to the pump, and isundesirable, since it can damage pump components, resulting indiminished pump capacity or pump failure.

To ensure that only single-phase liquid coolant is provided to the pump20, and thereby avoiding pump cavitation, the volume of coolant in thereservoir 200 can be selected to be a certain volume ratio of the totalvolume of coolant in the cooling apparatus 1. Increasing the volumeratio can increase the likelihood that any vapor bubbles 275 within thetwo-phase bubbly flow being delivered to the reservoir 200 from the oneor more heat sink modules 100 will have an opportunity to condense backto liquid before that quantity of coolant is drawn from the reservoir200 and delivered back to the pump inlet 21 for recirculation throughthe cooling apparatus 1. The preferred volume ratio can depend on avariety of factors, including, for example, the heat load associatedwith the surface being cooled 12, the properties of the coolant 50 beingused, the flow rate of coolant in the system, the flow quality (x) ofcoolant being returned to the reservoir 200, the percentage of coolantflow 51 being diverted through the first and second bypasses (305, 310),the operating pressure of the coolant, and the performance of the heatexchanger 40. In some examples, the volume ratio can be about 0.2-0.5,0.4-1.0, 0.6-1.5, 1.0-2.0, or greater than 2.0. It can be desirable toencourage condensing of any bubbles that may be delivered to thereservoir 200 as two-phase bubbly flow from the one or more heat sinkmodules 100. Experiments have shown that maintaining the reservoir 200at a fill level of about 30-90%, 40-80%, or 50-70%, (where fill level isdefined as the percent volume of the reservoir 200 occupied by liquidcoolant 50) results in effective condensing of bubbles 275 that aredelivered to the reservoir by the return line 230. A liquid-vaporinterface is established at the fill level of the reservoir 200, andthis liquid-vapor interface may encourage condensation of the bubbles275 due to hydrodynamic effects acting on the two-phase bubbly flow asit is delivered to (e.g. poured or sprayed into) the reservoir 200 andpasses through the liquid-vapor interface within the reservoir and mixeswith the sub-cooled single-phase liquid coolant residing in thereservoir. As shown in FIG. 3, the return line 230 carrying thetwo-phase bubbly flow can deliver the two-phase bubbly flow near anupper portion of the reservoir 200. In some examples, the delivery pointof two-phase bubbly flow to the reservoir 200 can be located above thefill level of the reservoir to ensure the two-phase bubbly flow isdelivered into the head space (i.e. vapor region) of the reservoir, suchthat gravity draws the two-phase bubbly flow downward through theliquid-vapor interface.

In some examples, the reservoir 200 can include a baffle positioned inthe head space of the reservoir or partially in the head space andpartially below the fill level (i.e. passing through the liquid-vaporinterface). The baffle can be configured to encourage condensing ofbubbles 275 in two-phase bubbly flow delivered to the reservoir 200. Thebaffle can span all or a portion of the reservoir 200 and can bepositioned horizontally, vertically, or obliquely within the reservoir.The baffle can be made of a thermally conductive material, such assteel, aluminum, or copper. When two-phase bubbly flow 51 is deliveredto the reservoir 200, the flow can pass through openings (e.g. aplurality of slots or holes) in the baffle, and heat can transfer fromthe two-phase bubbly flow to the baffle and, in some cases, to the wallsof the reservoir 200 to which the baffle is mounted or in contact with.As heat is transferred away from the two-phase bubbly flow, bubbles 275within the coolant 50 can condense, either due to decreases in the bulkfluid temperature in the reservoir or due to local decreases in fluidtemperature proximate the condensing bubbles. The openings in the bafflecan have any suitable shape. Non-limiting examples of baffle openingshapes include triangular, round, oval, rectangular, or hexagonal, orpolygonal.

Inlet and Outlet Manifolds

As shown in FIG. 12T, an inlet manifold 210 can receive coolant 50 andcan deliver the coolant to one or more flexible tubes 225 that deliverthe coolant to one or more heat sink modules 100 fluidly connectedbetween the inlet manifold 210 and an outlet manifold 215. The inletmanifold 210 can have an inner volume that serves as an in-linereservoir for the coolant and effectively dampens pressure pulsations inthe flow 51 of coolant that may be transmitted from the pump 20. In someexamples, the proper size of the inner volume of the inlet manifold 210can be determined by the flow rate of coolant 50 through the inletmanifold. For instance, the inner volume of the inlet manifold 210 maybe configured to hold a volume of coolant that is greater than or equalto a volume equivalent to at least 5 seconds of coolant flow through themanifold. So for a coolant flow rate of about 1 liter/minute, the inletmanifold 210 can have an inner volume of about 0.083 liters. Forsmoother operation, and greater damping of pressure pulsations, theinlet manifold 210 can have an inner volume capable of storing at least10, 15, 20, 60 or more seconds of coolant flow 51. The outlet manifold215 can be configured to have a similar internal volume as the inletmanifold 210 to provide similar damping of pressure pulsations betweenthe heat sink modules 100 and the return line 230.

FIG. 12T shows a schematic of a cooling apparatus 1 configured to cooltwo racks 410 of servers 400. The cooling apparatus 1 in FIG. 12T has asimilar configuration as the cooling apparatus 1 shown in FIGS. 1-3, butthe cooling apparatus 1 in FIG. 12T only shows two server racks 410,whereas the cooling apparatus in FIGS. 1-3 shows eight server racks 410.Also, the cooling apparatus 1 in FIG. 12T shows fewer parallel coolinglines extending between each inlet and outlet manifold (210, 215).Nevertheless, the overall concept is similar. The cooling apparatus 1 inFIG. 12T includes a dedicated inlet manifold 210 and outlet manifold 215for each server rack 410. This configuration provides a modular coolingsystem 1 that can be increased in size to accommodate additional serverracks 410, for example, as a data center 425 increases its server count.Therefore, the configuration in FIG. 12T can easily be modified toresemble the configuration shown in FIGS. 1-3 by adding six additionalserver racks 410 and by increasing the number of cooling lines extendingbetween each inlet and outlet manifold (210, 215).

FIG. 4 shows a rear side view of a server rack 410 with an inletmanifold 210 and outlet manifold 215 mounted vertically to the serverrack 410. The inlet manifold 210 and the outlet manifold 215 can befitted with a plurality of fittings 235, such as quick-connect fittings,that permit individual cooling loops 300 to be hot swapped withoutinterrupting coolant flow through other cooling loops 300 of theapparatus 1. As shown in FIG. 4, the inlet and outlet manifolds (210,215) can each include a plurality of fittings to permit a plurality ofcooling lines 300 to be connected to each manifold. In some examples,the inlet and outlet manifolds (210, 215) can include extra, unutilizedfittings 235, as shown in FIG. 4, to permit future expansion of thenumber of servers 400 cooled by the cooling apparatus 1.

Although the inlet and outlet manifolds (210, 215) are shown in avertical orientation in FIG. 4, this is not limiting. As discussedherein, because the vapor bubbles 275 within the two-phase bubbly floware effectively dispersed and suspended in the coolant flow and do notseek a high point in the cooling apparatus 1 in response togravitational effects, the system components (such as the outletmanifold 215) do not need to be vertically oriented to ensure collectionof vapor, as competing systems do. Consequently, the outlet manifold 215can be oriented horizontally or at any other suitable orientation thatis preferable for a particular installation in view of space constraintsand manifold size.

Flexible Tubing

FIG. 5 shows a top perspective view of a server 400 with its lid removedand a portion of a cooling apparatus 1 having a primary cooling loop 300installed within the server housing. The cooling loop 300 can include acooling line 303 connected to two heat sink modules 100 mounted onvertically oriented heat-generating components (e.g. GPUs) within theserver 400. The heat sink modules 100 are arranged in a seriesconfiguration and are fluidly connected with sections of flexible tubing225 to transport coolant between neighboring heat sink modules, from anoutlet port 105 of the first heat sink module 100 to an inlet port 105of the second heat sink module. In some examples, others types of tubingcan be used, such as smooth tubing 225, as shown in FIGS. 4, 84, and 85.More specifically, smooth nylon or fluorinated ethylene propylene (FEP)tubing 225 can be used. In one example, the flexible tubing 225 can beFEP tubing from Cole-Parmer of Vernon Hills, Ill. and can have a maximumtemperature rating of about 400 degrees F., an inner diameter of about0.25-0.375 inches, and a maximum working pressure of about 210 psi. Inanother example, the flexible tubing 225 of the cooling lines 303 can befluoropolymer tubing from SMC Corporation of Tokyo, Japan and can have amaximum operating pressure of about 60-75 psi at 100 degrees C., aninner diameter of about 0.165-0.185 inches, and a minimum bend radius ofabout 2.0-2.5 inches. The flexible tubing 225 can be chemically inert,nontoxic, heat resistant, and have a low coefficient of friction. Inaddition, the flexible tubing 225 may not noticeably deteriorate withage.

Providing a cooling apparatus 1 that operates at low pressures (e.g.less than 50 psi) as described herein, allows low pressure, flexibletubing 225 to be used, which is significantly less expensive than highpressure tubing, such as braided stainless steel tubing. Moreover,operating at lower pressures reduces power consumption by the pump 20,which provides a more efficient cooling system 1. Low pressure lines 225can have substantially smaller minimum bend radiuses R and substantiallysmaller outer diameters than high pressure lines, making them far easierto route within server housings 400 where space is limited and wheretight bends are commonly required to route around server components,such as fans and power electronics, as shown in FIG. 84.

In some applications, corrugated, flexible tubing 225 can providecertain advantages. For instance, corrugated tubing can resist kinkingwhen routed in space-constrained applications, such as within servers400 as shown in FIGS. 5 and 6. Flexible, corrugated tubing can be routedin configurations where the tubing contains bends that result in180-degree directional changes without kinking, as shown in FIG. 6. Insome examples, the flexible, corrugated tubing 225 can be corrugated FEPtubing from Cole-Parmer and can have a maximum temperature rating ofabout 400 degrees F. and a maximum working pressure of about 250 psi.

An advantage of corrugated tubing 225 is that, when transportingtwo-phase bubbly flow, it may delay the onset of slug flow by causingthe breakdown of larger bubbles into smaller bubbles and causing thebreakdown of clusters of bubbles due to frictional effects acting on thebubbles as they pass through the corrugated tubing and contact the innerwalls of the tubing. Slug flow occurs when one or more large orbullet-shaped bubbles of vapor form within the tubing 225. As shown inFIG. 58, large vapor bubbles within slug flow may be nearly as wide asthe inner diameter of the tubing. Slug flow is undesirable, since it cancreate flow instabilities in the cooling apparatus 1, resulting insurging or chugging within the cooling loops 300, making it difficult tomaintain desired pressures in certain components of the cooling system1, such as the heat sink modules 100, and thereby making it difficult toprovide consistent and predictable cooling of a heated surface 12. Slugflow can be combatted by increasing the flow rate through the heat sinkmodules 100 to reduce flow quality (x) (due to less vapor formation),thereby restoring two-phase bubbly flow, for example, betweenseries-connected heat sink modules 100. In some examples, the coolingapparatus 1 can be configured to detect the onset of slug flow (e.g.using a visual flow detection system) at an outlet port 110 of a heatsink module 100 or at some other point in the cooling loop 300 and toautomatically increase the coolant flow rate 51 to restore two-phasebubbly flow at the outlets of the one or more heat sink modules 100.

Another advantage of corrugated tubing 225 is that it can resistcollapse when vacuum pressure is applied to an inner volume of thetubing. Vacuum pressure may be applied to the tubing 225 duringservicing of the cooling apparatus 1. For example, when draining coolant50 from the system 1 to allow for repairs or maintenance to beperformed, vacuum pressure can be applied to a location (e.g. a drain245) in the cooling apparatus 1 to draw out coolant 50 from the tubesand components of the apparatus. Portions of the cooling apparatus 1 canthen be safely disassembled without having to make other arrangementsfor containment of the coolant. Removing coolant 50 through theapplication of vacuum pressure can allow the coolant to be captured in avessel and reused to fill the apparatus when servicing is complete,thereby reducing servicing costs and waste that would otherwise beassociated with discarding and replacing the coolant.

FIG. 6 shows a top view of a server 400 with its lid removed and aportion of a cooling apparatus 1 visible within the server. This exampleof a server 400 includes a motherboard 405, two microprocessors 415, andtwo sets of three memory modules 420. The two microprocessors 415 aremounted parallel to the motherboard 405, and the memory modules 420 aremounted perpendicular to the motherboard 405. The cooling apparatus 1includes two heat sink modules 100 arranged in a series configurationand fluidly connected by flexible sections of flexible tubing 225. Thefirst heat sink module 101 is mounted on a first microprocessor, and thesecond heat sink module 102 is mounted on a second microprocessor. Afirst section of flexible tubing 225 delivers coolant the an inlet port105 of the first heat sink module 101, and a second section of flexibletubing 225 delivers coolant from an outlet port 110 of the first heatsink module 101 to an inlet port 105 of the second heat sink module 102.As, shown, due to its flexibility, the second section of flexible tubing225 can easily be routed around server components for ease ofinstallation. The flexible tubing 225 can be arranged in a variety ofconfigurations, including serpentine configurations, to allow any twoheat sink modules 100 (e.g within a server housing) to be fluidlyconnected regardless of the orientation or placement of the two heatsink modules.

The heat sink modules 100 can be used within the server 400 to coolelectrical components that produce the most heat, such as themicroprocessors 415. Other components within the server 400 may alsoproduce heat, but the amount of heat produced may not justifyinstallation of additional heat sink modules 100. Instead, to removeheat generated by other electrical devices within the server 400, one ormore fans 26 can be used to expel warm air from the server 400 housing,as shown in FIG. 6. The fans can be configured to draw cool room airinto the server housing 400 and to expel warm air from the housing.

In some examples, the length of a section of flexible tubing 225 betweenseries-connected modules can be at least 4, 6, 12, 18, or 24 inches inlength. In some applications, increasing the length of the section oftubing 225 can promote condensation of bubbles 275 within the bubblyflow between series-connected heat-sink modules due to heat transferfrom the liquid to the tubing 225 and ultimately from the tubing to theambient air, as well as heat transfer within the coolant from the vaporportion of the flow to the liquid portion of the flow, thereby elevatingthe bulk fluid temperature as vapor bubbles collapse. In someapplications, increasing the length of the second section of flexible,corrugated tubing 225 may promote breaking apart of clusters of bubblesthat may form in the two-phase flow, thereby delaying the onset ofplug/slug flow and maintaining two-phase bubbly flow.

Coolant Filter

FIG. 13 shows a schematic of a cooling apparatus 1 including a filter260 located between the reservoir 200 and the pump 20 in the primarycooling loop 300. The filter 260 can trap and prevent debris fromentering and damaging the pump 20. Likewise, the filter 260 can trap andprevent debris from passing through the primary cooling loop 300 to theone or more heat sink modules 100, where the debris could potentiallyclog small orifices 155 in the heat sink modules. The cooling apparatus1 can include one or more filters 260 placed upstream or downstream ofthe pump 20, or in any other suitable locations. The filter 260 can beconnected inline using quick-connect fittings. The filter 260 can be adisposable filter or a reusable filter. The filter can have a micronrating of about 5, 10, or 20 microns.

In some examples, the heat sink module 100 can include a filter 260 toensure that no debris is permitted to enter the heat sink module andclog orifices 155 within the heat sink module. The filter 260 can bedisposed within the heat sink module (e.g. a removable filter that isinserted within the inlet port 105, inlet passage 165, or inlet chamber145), or can be attached in-line with the heat sink module 100, such asa filter component that is threaded onto the inlet port and thatcontains a filtration device. By placing the filter 260 in orimmediately upstream of the heat sink module 100, clogging of orifices155 within the heat sink module can be avoided regardless of wheredebris originates from in the cooling apparatus 1.

Heat Sink Module

The heat sink module 100 can be configured to mount on a surface to becooled 12 and provide a plurality of jet streams 16 (e.g. an array ofjet streams 16) of coolant that impinge against the surface to be cooled12 to effectively remove heat from the surface to be cooled. By removingheat from the surface to be cooled 12, the heat sink module 100 caneffectively maintain the temperature of the surface to be cooled 12 at asuitable level so that a device associated with the surface to be cooled12 is able to operate without overheating (i.e. operate below athreshold temperature).

The heat sink module 100 can include a top surface 160 and a bottomsurface 135 opposite the top surface. The heat sink module 100 can beuniquely sized and shaped for a particular application. For instance,where the heat sink module 100 is tasked with cooling a square-shapedmicroprocessor, the heat sink module 100 can have a square perimeter, asshown in FIGS. 21-24. In this example, the heat sink module 100 can bedefined by a front side surface 175, a rear side surface 180, a leftside surface 185, a right side surface 190, the top surface 160, and thebottom surface 135. In other applications, the perimeter shape of theheat sink module 100 can be round, polygonal, or non-polygonal. In someexamples, the heat sink module 100 can have dimensions that allow it toreplace a traditional finned heat sink. For instance, the heat sinkmodule 100 can have a footprint of about 91.5×91.5 mm or 50×50 mm. Inother examples, the heat sink module can be sized for a specific CPU orGPU. The features of the heat sink module 100 are scalable and can berapidly manufactured using a 3D printing process.

The heat sink module 100 can have any suitable sealing feature locatedon the bottom surface 135 to facilitate sealing against the surface tobe cooled 12 or against an intermediary surface, such as a surface of athermally-conductive base member (e.g. a copper plate 430) that isadhere to the surface to be cooled 12. In some examples, the heat sinkmodule 100 can include a channel 140 along its bottom surface 135, asshown in FIG. 24. The channel 140 can be configured to receive asuitable sealing member 125, such as a gasket or O-ring, as shown inFIG. 23. In some examples, the channel 140 can be a continuous channelthat circumscribes an outlet chamber 150 of the heat sink module 100, asshown in FIG. 24. In other examples, the heat sink module 100 caninclude alternate or additional sealing materials, such as a liquidgasket material, a die cut rubber gasket, an adhesive sealant, or a 3-Dprinted gasket provided on the bottom surface 135 of the heat sinkmodule 100.

Although the bottom surface 135 of the heat sink module shown in FIG. 23is flat, this is non-limiting. For applications involving a contouredsurface to be cooled 12, the bottom surface 135 of the heat sink module100 can have a corresponding contour that matches the contour of thesurface to be cooled 12 and a thereby allows a sealing member 125disposed therebetween to provide a liquid tight seal. In one example,the bottom surface 135 of the heat sink module can have a contourconfigured to match an external surface contour of a cylindrical tube orvessel (e.g. a metallic vessel) used in a chemical process, such as acondensation process or cooling wort in a brewing process. The contouredbottom surface 135 of the heat sink module 100 can allow the heat sinkmodule to be form a liquid-tight seal against the tube or vessel andcool an external surface of the tube or vessel that is exposed withinthe outlet chamber 150 of the heat sink module 100. Where the contentsof a large vessel must be cooled rapidly, such as when chilling wort ina brewing process, a plurality of heat sink modules 100 can be arrangedon the external surface(s) of the large vessel to remove heat from thevessel rapidly, thereby allowing the cooling apparatus 1 to replace aglycol chiller system in a modern brewery or a counterflow chiller(which uses a significant amount of chilled water) in a more traditionalbrewery.

The heat sink module 100 can include mounting holes 130 or locatingholes, as shown in FIGS. 21 and 23, located near corners of the moduleand/or along one or more perimeter portions of the module. Fasteners 115can be inserted through the mounting holes 130, as shown in FIG. 22, andinstalled into threaded holes associated with a mounting surface towhich the heat sink module 100 is mounted, such as a mounting surface ofa thermally conductive base member 430 (e.g. a copper base plate) ordirectly to a mounting surface of an electrical device (e.g. amicroprocessor 415 or a motherboard 405). In some examples, screw-typefasteners 115 can be replaced with alternate types of fastening devicesthat allow for faster installation and/or removal of the heat sinkmodule 100. In one example, the heat sink module 100 can be fastened toa heat source using a buckle mechanism, similar a ski boot buckle, toallow for rapid, tool-less installation. In other examples, the heatsink module 100 can be received by a snap fitting on the surface to becooled 12, thereby allowing the heat sink module to be installed anduninstalled with ease by hand and without tools.

During installation of the heat sink module 100 on a surface to becooled 12, one or more fasteners 115 can be inserted through one or more130 holes in the heat sink module, and the one or more fasteners canengage mounting holes in the surface 12 to permit secure mounting of theheat sink module 100 to the surface 12. As the fasteners 115 aretightened, the heat sink module 100 can be drawn down tightly againstthe surface to be cooled 12, and the sealing member 125 (e.g. o-ring orgasket) can be compressed between the surface and the channel 140. Uponcompression, the sealing member 125 can provide a liquid-tight seal toensure that coolant 50 does not leak from the outlet chamber 150 duringoperation of the cooling system 1 as coolant 50 flows from the inletport 105 to the outlet port 110 of the heat sink module 100.

The heat sink module 100 can include an inlet port 105, as shown in FIG.21. The inlet port 105 can have internal or external threads 170 thatallow a connector 120 to be connected to the inlet port. Any suitableconnector 120 can be used to connect the inlet section of flexibletubing 225 to the inlet port 105. In some examples, as shown in FIG. 22,a metal or polymer connector 120 from Swagelock Company of Solon, Ohiocan be used to connect the flexible tubing to the inlet port 105. Thetop surface 160 of the heat sink module 100 can include visual markings132 to identify a preferred flow direction through the heat sink moduleto ensure proper routing of tubing to and from the heat sink module 100to ensure that coolant flow 51 is delivered to the inlet port 105 andexits from the outlet port 110 and is not accidentally reversed.

As shown in FIG. 25, the heat sink module 100 can include an inletpassage 165 that fluidly connects the inlet port 105 to an inlet chamber145 of the heat sink module. The heat sink module 100 can include adividing member 195 that separates the inlet chamber 145 from the outletchamber 150. The dividing member 195 can have a top surface and a bottomsurface and can include one or more orifices 155 passing from the topsurface to the bottom surface of the dividing member. The orifices 155permit jet streams 16 of coolant 50 to be emitted from the bottomsurface of the dividing member 195 and into the outlet chamber 150 whenpressurized coolant 54 is delivered to the inlet chamber 145, as shownin FIG. 26.

As shown in the cross-sectional view of FIG. 25, the inlet chamber 145can have a geometry that tapers in cross-sectional area from the frontside surface 175 of the heat sink module 100 toward the rear sidesurface 180 of the heat sink module. The tapered cross-sectional area ofthe inlet chamber 145 can ensure that all orifices 155 receive coolant50 at a similar pressure. Similarly, the outlet chamber 150 can increasein cross-sectional area in a direction from the rear surface 180 of theheat sink module toward the front surface 175 of the heat sink module100. The increase in cross-sectional area of the outlet chamber 150 canprovide suitable volume for expansion of the coolant that may occur as aportion of the liquid coolant transitions to vapor, as shown in FIG. 30,and exits the outlet port 110 of the heat sink module 100.

The heat sink module 100 can include one or more inlet passages 165 topermit fluid to enter the inlet chamber 145 and one or more outletpassages 166 to permit fluid to exit the outlet chamber 150. In thismanner, the heat sink module 100 can be configured to permit fluid toflow through the outlet chamber 150. A dividing member 195 can at leastpartially separate the inlet chamber 145 from the outlet chamber 150. Aplurality of orifices 155 can be formed in the dividing member as shownin FIGS. 24 and 25. The plurality of orifices 155 can be configured toeach project a stream 16 of coolant 50 against the surface to be cooled12. In some examples, the streams 16 of fluid projected against thesurface 12 can be jet streams. As used herein, a “jet” or “jet stream”refers to a substantially liquid fluid filament that is projectedthrough a substantially liquid or fluid medium or a mixture thereof. Asused herein, a “jet stream” can include a single-phase liquid fluidfilament or a two-phase bubbly flow filament. “Jet” or “jet stream” iscontrasted with “spray” or “spray stream,” where “spray” or “spraystream” refers to a substantially atomized liquid fluid projectedthrough a substantially vapor medium.

The inlet chamber 145 and the outlet chamber 150 can be formed withinthe heat sink module 100. The heat sink module 100 can be made from anysuitable material and manufactured by any suitable manufacturingprocess. In some examples, the heat sink module 100 can be made of apolymer material and formed through a 3D printing process, such asstereolithography (SLA) using a photo-curable resin. Printers capable ofproducing heat sink modules as shown in FIGS. 21-54 are available from3D Systems Corporation of Rock Hill, S.C. In other examples, a modulebody can be injection molded to reduce cost and manufacturing time andan insertable orifice plate can be 3-D printed and attached to themodule body to complete the heat sink module 100.

The heat sink module 100 can be configured to cool a surface 12 of aheat source. The heat sink module 100 can include an inlet chamber 145formed within the heat sink module and an outlet chamber 150 formedwithin the heat sink module. In some examples, the outlet chamber 150can have an open portion along the bottom side surface 135 of the heatsink module 100, as shown in FIG. 23. The open portion of the outletchamber 150 can be enclosed by the surface 12 of a heat source when theheat sink module 100 is installed on the surface 12 of the heat source,as shown in FIG. 26. The heat sink module 100 can include a dividingmember 195 disposed between the inlet chamber 145 and the outlet chamber150. The dividing member 195 can include a first plurality of orifices155 formed in the dividing member. The first plurality of orifices 155can pass from a top side of the dividing member 195 to a bottom side ofthe dividing member and can be configured to deliver a plurality of jetstreams 16 of coolant 50 into the outlet chamber 150 when pressurizedcoolant 54 is provided to the inlet chamber 145, as shown in FIG. 26.

The first plurality of orifices 155 can have any suitable diameter thatallows the orifices to provide well-formed jets streams 16 of coolant 50when pressurized coolant 54 is delivered to the inlet chamber 145 of theheat sink module 100. In some examples, the orifices 155 may all haveuniform diameters, and in other examples, the orifices may not all haveuniform diameters. In either case, the average diameter of the orifices155 can be about 0.001-0.020, 0.001-0.2, 0.001-0.150, 0.001-0.120,0.001-0.005, 0.020-0.045, 0.030-0.050 in, or 0.040 in. An orifice 155diameter of about 0.040 in. can be preferable to ensure that orificeclogging does not occur.

In some examples, to ensure that well-formed jet streams 16 of coolant50 are provided by the orifices 155, the length of the orifice can beselected based on the diameter of the orifice. For instance, where thefirst plurality of orifices 155 are defined by a diameter D and anaverage length L, in some cases L divided by D can be greater than orequal to one, about 1-10, 1-8, 1-6, 1-4, 1-3, or 2. In the configurationshown in FIG. 26, the length of each orifice 155 can be determined basedon an angle of the orifice with respect to the surface to be cooled 12and based on the thickness of the dividing member 195. In some examplesthe dividing member 195 can have a thickness of about 0.005-0.25,0.020-0.1, 0.025-0.08, 0.025-0.075, 0.040-0.070, 0.1-0.25, 0.040-0.070,or 0.080 in. The thickness of the dividing member 195 can be selected toprovide a desired length for the orifices 155 to ensure columnar jetstreams 16 of coolant. The thickness of the dividing member can also beselected to ensure structural integrity of the heat sink module 100 whenreceiving pressurized coolant 54 in the inlet chamber 145 and towithstand vacuum pressure when coolant 50 is purged from the coolingsystem 1. To minimize the height of the heat sink module 100 (e.g. toprovide greater freedom when dealing with tight packaging constraints),it can be desirable to select a minimal dividing member thickness thatstill provides well-formed columnar jet streams 16 and adequatestructural integrity.

The heat sink module 100 can be made of any suitable material or process(e.g. a three-dimensional printing process) and can have any suitablecolor or can be colorless. In some examples, it may be desirable tovisually inspect the operation of the heat sink module 100 to ensurethat boiling is occurring within the heat sink module proximate thesurface to be cooled 12. To permit visual inspection, at least a portionof the heat sink module 100 can be made of a transparent or translucentmaterial. In some examples, the transparent or translucent material canform the entire heat sink module 100, and in other examples, thetransparent or translucent material can form only a portion of the heatsink module, such as a window into the outlet chamber 150 of the heatsink module or a side wall of the heat sink module. In these examples,the window or side wall can permit boiling coolant within the outletchamber 150 to be observed when the heat sink module 100 is installed onthe surface to be cooled 12.

Orifices within Heat Sink Module

Each orifice 155 within the heat sink module 100 can include a centralaxis 74, as shown in FIG. 30. The central axis 74 of the orifice 155 mayeither be angled perpendicularly with respect to the surface to becooled 12 or angled non-perpendicularly with respect to the surface tobe cooled 12, the latter of which is shown in FIG. 30. FIG. 20 shows across-sectional view of a heat sink module with orifices 155 arranged ata 45-degree angle with respect to the surface to be cooled 12. If anglednon-perpendicularly with respect to the surface to be cooled 12, thecentral axis 74 of the orifice 155 may define any angle between 0° and90° with respect to the surface 12, such as about 5°, about 10°, about15°, about 20°, about 25°, about 30°, about 35°, about 40°, about 45°,about 50°, about 55°, about 60°, about 65°, about 70°, about 75°, about80° or about 85° or any range therebetween (e.g. 5-15°, 10-20°, 15-25°,20-30°, 25-35°, 30-40°, 35-45°, 40-50°, 45-55°, 50-60°, 55-65°, 60-70°,65-75°, 70-80°, or 75-85°). The orifice 155 can have any cross-sectionalshape when viewed along its central axis 74. Various examples include acircular shape, an oval shape (to generate a fan-shaped jet stream), apolygonal shape, or any other suitable cross-sectional shape.

FIG. 31 shows a top cross-sectional view of the heat sink module of FIG.21 taken along section C-C shown in FIG. 25. Section C-C passes throughthe dividing member 195 and exposes the array 76 of orifices 155 withinthe heat sink module 100. In this example, because the central axes 74of the plurality of orifices are arranged at a 45-degree angle withrespect to the dividing member 195, the orifices appear as ovals in FIG.31 despite the orifice being cylindrical coolant passageways through thedividing member.

The heat sink module 100 preferably includes an array 76 of orifices155. The central axes 74 of the orifices 155 in the array 76 may definedifferent angles with respect to the surface to be cooled 12.Alternately, the central axis 74 of each orifice 155 in the array 76 mayhave the same angle with respect to surface 12, as shown in FIG. 30. Insome examples, providing neighboring orifices with central axes 74 withthe same angle with respect to the surface to be cooled 12 can bepreferable to avoid interaction (i.e. interference) of the jet streams16 prior to impingement on the surface to be cooled 12. By providing jetstreams 16 of coolant that do not interfere with each other prior toimpingement, the heat sink module 100 can provide jet streams 16 withsufficient momentum to disrupt vapor formation on the surface to becooled 12, thereby increasing the three-phase contact line 58 length onthe surface to be cooled 12 and allowing higher heat fluxes to beeffectively dissipated without reaching critical heat flux (see, e.g.FIG. 63).

The array 76 of orifices 155 may be arranged in any configurationsuitable for cooling the surface to be cooled 12. FIG. 62 shows possibleorifice 155 configurations including (a) a regular rectangular jet array76, (b) a regular hexagonal jet array 76, and (c) a circular jet array76. In the regular hexagonal array 76, shown in FIGS. 23, 31 and 62(b),the arrays 76 can be organized into staggered columns 77 and rows 78.The staggering of orifices 155 in the array 76 is such that a givenorifice 155 in a given column 77 and row 78 does not have acorresponding orifice in a neighboring row 78 in the given column 77 ora corresponding orifice 155 in a neighboring column 77 in the given row78. If the orifices 155 are configured to induce a substantially samedirection of flow 90 along the surface to be cooled 12 (as shown inFIGS. 30 and 32), the columns 77 and the rows 78 are preferably orientedsubstantially parallel and perpendicular, respectively, to thesubstantially same direction of flow 90. Arrays of orifices 155 innon-staggered arrangements can be used in other examples of the heatsink module 100.

The orifice 155 can be configured to project a jet stream 16 having anyof a variety of shapes and any of a variety of trajectories. With regardto shape, the stream 16 is preferably a symmetrical stream. As usedherein, “symmetrical stream,” refers to a jet stream 16 that issymmetrical in cross section. Examples of symmetrical streams includelinear streams, fan-shaped streams, and conical streams. Linear streamshave a substantially constant cross section along their length. Conicalstreams have a round cross section that increases along their length.Fan-shaped streams have a cross section along their length with a firstcross-sectional axis being significantly longer than a second,perpendicular cross-sectional axis. In some versions of the conical jetstreams 16, at least one and possibly both of the cross-sectional axesincrease in length along the length of the stream. With regard totrajectory, the jet stream 16 preferably includes a central axis 17. Forthe purposes herein, the “central axis 17 of the stream 16” is the lineformed by center points of a series of transverse planes taken along thelength of the stream 16, where each transverse plane is oriented tooverlap with the smallest possible surface area of the stream 16, andeach center point is the point on the transverse plane that isequidistant from opposing edges of the stream 16 along the transverseplane. In preferred versions, the orifice 155 projects a jet stream 16having a central axis 17 that is substantially collinear with thecentral axis 74 of the orifice 155. However, the orifice 155 may alsoproject a stream 16 having a central axis 17 that is angled with respectto the central axis 74 of the orifice 155. The angle of the central axis17 of the stream 16 with respect to the central axis 74 of the orifice155 may be any angle between 0° and 90°, such as about 1°, about 2°,about 3°, about 4°, about 5°, about 7°, about 10°, about 15°, about 20°,about 25°, about 30°, about 35°, about 40°, about 45°, about 50°, about55°, about 60°, about 65°, about 70°, about 75°, or about 80° or anyrange therebetween. In such versions, the orifice 155 preferablyprojects a jet stream 16 where at least one portion of the jet stream 16is projected along the central axis 74 of the orifice 155. However, theorifice 155 may also project a jet stream 16 where no portions of thejet stream 16 are projected along the central axis 74 of the orifices155.

Similarly, the orifice 155 may be configured to project a jet stream 16that impinges on the surface 12 at any of a variety of angles. In someversions, the orifice 155 projects a stream 16 at the surface 12 suchthat the entire stream (in the case of a linear stream), or at least thecentral axis 17 of the stream 16 (in the case of conical or fan-shapedstreams), impinges perpendicularly on the surface 12 (i.e., at a 90°angle with respect to the surface). Perpendicular impingement upon asurface 12 induces radial flow of coolant 50 from contact points alongthe surface 12. While arrays 96 of perpendicularly impinging streams 16are suitable for some applications, they are not optimal in efficiency.This is because opposing coolant flow from neighboring contact pointsinteracts to form stagnant regions. Heat transfer performance in thesestagnant regions can fall to nearly zero, which in high heat fluxapplications (e.g. cooling high performance microprocessors or powerelectronics) can pose risks associated with critical heat flux.

In a preferred examples shown in FIGS. 30 and 32, the orifices 155 areconfigured to project jet streams 16 of coolant that impinge the surfaceto be cooled 12 such that at least the central axis 17 of each jetstream 16, and more preferably the entire jet stream 16, impingesnon-perpendicularly on the surface to be cooled 12 (i.e. at an angleother than 90° with respect to the surface), as shown in FIGS. 30-32. Asa non-limiting example, the central axis 17 of the jet stream 16 mayimpinge on the surface 12 at any angle between 0° and 90°, such as about1°, about 2°, about 3°, about 4°, about 5°, about 7°, about 10°, about15°, about 20°, about 25°, about 30°, about 35°, about 40°, about 45°,about 50°, about 55°, about 60°, about 65°, about 70°, about 75°, orabout 80° or any range there between.

FIG. 32 depicts a top view of a surface 12 on which jet streams 16 of anarray 76 of jet streams impinges non-perpendicularly on the surface 12.The non-perpendicular impingement creates a flow pattern 90 to the rightin which all the coolant 50 flows along the surface 12 in substantiallythe same direction 90. In some versions of patterns flowing insubstantially the same direction 90, flow of coolant 50 at each portionof the surface 12 has a common directional vector component along aplane defined by the surface to be cooled 12. In other versions, coolant50 at no two points on the surface 12 flows in opposite directions. Inyet other versions, coolant 50 at no two points on the surface 12 flowsin opposite directions or flows in perpendicular directions. Flowingcoolant 50 in the substantially same direction eliminates stagnantregions on the surface being cooled 12, which helps avoid the onset ofcritical heat flux.

The plurality of orifices 155 in the array 76 are preferably configuredto provide impinging jet streams 16 of coolant on the surface 12 in anarray 96 of contact points 91 (i.e. where each contact point 91 is a jetstream 16 impingement location on the surface to be cooled 12) havingstaggered columns 97 and rows 98, as shown in FIG. 32. The staggering issuch that a given contact point 91 in a given column 97 and row 98 doesnot have a corresponding contact point 91 in a neighboring column 97 inthe given row 98 or a corresponding contact point 91 in a neighboringrow 98 in the given column 97. If the coolant 50 is induced to flowacross the surface 12 in substantially the same direction 90, as shownin FIG. 32, either the columns 97 or the rows 98 are preferably orientedsubstantially perpendicularly to the substantially same direction 90 offlow. Arrays 96 of contact points 91 arranged in this manner permitcoolant 50 emanating from each contact point 91 in a given column 97 orrow 98 to flow substantially between contact points 91 in a neighboringcolumn 97 or row 98, respectively, as shown in FIG. 32. The heat sinkmodule 100 shown in FIGS. 21 and 30 provides even, consistent flow ofcoolant 50 over the surface to be cooled 12, without formation ofstagnation regions, and thereby encourages bubble 275 generation andevaporation, which dramatically increases the heat transfer rate fromthe surface to be cooled 12.

The heat sink module 100 can include an array 76 of orifices 155 witheach orifice 155 having a central axis 74 angled non-perpendicularlywith respect to the surface 12, where each orifice 155 projects a jetstream 16 of coolant 50 having a central axis 17 collinear with thecentral axis 74 of the orifice 155. In some examples, all the orifices155 can have central axes 74 oriented at about the same angle and canproject jet streams 16 of coolant having about the same trajectory andshape and can impinge against the surface 12 at about the same angle ofimpingement.

The array 76 of orifices 155 can be provided within the heat sink module100 as illustrated and described with respect to FIGS. 23-31. Theplurality of jet streams 16 emitted from the plurality of orifices 155can promote bubble generation and evaporation at the surface to becooled 12, thereby achieving higher heat transfer performance thanconventional single-phase liquid cooling systems. Other implementationsmay promote bubble 275 generation using structures within the orifices155, such as structures that encourage cavitation or degassing ofnon-condensable gasses absorbed in the liquid. Similarlyboiling-inducing members 196 can be included in the heat sink module100, as shown in FIGS. 45-50, or can be included on the surface to becooled 12, as shown in FIG. 55.

Jet Streams with Entrained Bubbles

In some examples, it can be desirable provide jet streams 16 thatcontain entrained bubbles 275 to seed nucleation sites on the surface tobe cooled 12. Seeding nucleation sites on the surface to be cooled 12can promote vapor formation and can increase a heat transfer rate fromthe surface to be cooled 12 to the coolant 50. FIG. 73 shows a firstheat sink module 100 fluidly connected to a second heat sink module 100.A section of flexible tubing 225 transports coolant from an outlet port110 of the first heat sink module 100 to an inlet port 105 of the secondheat sink module 100. Within the first heat sink module 100, a pluralityof jet streams 16 of coolant are shown impinging a first surface to becooled 12. Due to heat transferring from the first surface to be cooled12 to the coolant 50 within in the outlet chamber 150 of the first heatsink module 100, vapor bubbles 275 form in the coolant 50. The bubbles275 can be dispersed within the liquid coolant as it exits the outletport 110 of the heat sink module 100. As the coolant 50 flows within thetubing 225 toward the inlet port 105 of the second heat sink module,some of the bubbles 275 may coalesce and form larger bubbles. The smalland large bubbles 275 can be transported to an inlet chamber 145 of thesecond heat sink module. The small bubbles may be sufficiently small totravel through the orifices 155 and become entrained in a jet streamthat impinges against the surface to be cooled. When the small bubblesimpinge the surface to be cooled 12, they may seed nucleation sites onthe surface to be cooled 12 and promote vapor formation, which canprovide higher heat transfer rates. In some examples, as shown in FIG.73, the larger bubbles 276 may be too large to pass through the orifices155. But pressure and flow forces may draw the larger bubbles 276 towardthe orifices 155, where upon contacting the orifice inlets, the largerbubbles 276 break into smaller bubbles that can pass through theorifices 155 and be entrained in the jet streams 16. In this way, thesize of the orifice 155 determines the maximum bubble size that will beentrained in the jet stream 16 and will impinge the surface to be cooled12. To provide jet streams 16 with entrained bubbles 275 that providedesirable seeding of nucleation sites on the surface to be cooled 12,the orifice 155 diameters within the heat sink module 100 can be about0.001-0.020, 0.001-0.2, 0.001-0.150, 0.001-0.120, 0.001-0.005, or0.030-0.050 in.

Anti-Pooling Orifices

Pooling of coolant 50 within the outlet chamber 150 of the heat sinkmodule 100 is undesirable, since it can create stagnation regions orother undesirable flow patterns that result in non-uniform cooling ofthe surface to be cooled 12, which can lead to critical heat fluxissues. To avoid pooling of coolant 50 in the outlet chamber 150, theheat sink module 100 can include a second plurality of orifices 156extending from the inlet chamber 145 to a rear wall (or proximate therear wall) of the outlet chamber 150, as shown in FIGS. 33-38. Thesecond plurality of orifices 156 can be configured to deliver aplurality of anti-pooling jet streams 16 of coolant to a rear portion ofthe outlet chamber 150 when pressurized coolant 54 is provided to theinlet chamber 145. As shown in FIG. 33, the second plurality of orifices156 can be arranged in a column along the rear wall of the outletchamber 150 thereby preventing coolant from pooling near the rear wallof the outlet chamber 150.

FIG. 35 shows a detailed view of one anti-pooling orifice 156 taken fromthe cross-sectional view of FIG. 34. The anti-pooling orifice 156 can beconfigured to deliver an anti-pooling jet stream 16 of coolant to a rearregion of the outlet chamber 150 to prevent coolant from pooling orstagnating near the rear wall of the outlet chamber 150. The centralaxes 75 of the anti-pooling orifice 156 can be arranged at an angle ofabout 0-90, 40-80, 50-70, or 60 degrees respect to the surface to becooled 12. In some examples, the central axes 75 of the anti-poolingorifice 156 can be at a larger angle than the central axes 74 of theplurality of orifices 155, as shown in FIG. 35. This arrangement canprevent interaction of the anti-pooling jet stream with a neighboringjet stream 16 prior to impingement on the surface to be cooled 12,thereby decreasing the likelihood of stagnation points on the surface tobe cooled 12 near the rear wall of the outlet chamber 150.

Boiling-Inducing Features

As described above, achieving boiling of coolant 50 proximate thesurface to be cooled 12 can dramatically increase the heat transfer rateand overall performance of the cooling apparatus 1. To encourage boilingof coolant 50 within the outlet chamber 150, the heat sink module 100can include one or more boiling-inducing members 196 extending from thebottom surface of the dividing member 195 toward the surface to becooled 12, as shown in FIG. 46. The one or more boiling-inducing members196 can be slender members extending from the bottom surface of thedividing member 195. In some examples, the one or more boiling-inducingmembers 196 can be configured to contact the surface to be cooled 12. Inother examples, the one or more boiling-inducing members 196 can beconfigured to extend toward the surface to be cooled but not contact thesurface to be cooled. Rather, a clearance can be provided between theone or more boiling-inducing members 196 and the surface to be cooled196, such that coolant 50 can flow between the surface to be cooled 12and the tips of the boiling-inducing members, thereby ensuring that nohot spots or stagnation regions are created on the surface to be cooled12. The clearance distance can be any suitable distance, and in someexamples can be 0.001-0.0125, 0.001-0.05, 0.001-0.02, 0.001-0.01, or0.005-0.010 in.

Angled Inlet and Outlet Ports

The inlet port 105 and outlet port 110 of the heat sink module 100 canbe angled to provide ease of installation in a wide variety ofapplications. For instance, when installing the heat sink module 100 ona microprocessor 415 that is mounted on a motherboard 405, as shown inFIG. 27, if the inlet port 105 of the heat sink module is arranged at anangle (a) that is greater than zero, a clearance distance is providedbetween a bottom surface of the inlet port 105 and the microprocessor415 and motherboard 405. This clearance distance can allow a connector120, such as a compression fitting, to be easily installed (e.g.threaded) on the inlet port 105) without interfering with or contactingthe microprocessor or motherboard. In addition, angling the port upwardsat a moderate angle reduces the likelihood that the heat sink module 100(and flexible tubing 225 connected to the inlet port 105) will interferewith any motherboard devices (e.g. capacitors, resistors, inductors),while still maintaining a compact height that allows the heat sinkmodule 100 to be used between two expansion cards. In the example shownin FIG. 21, a height measured from the bottom surface 135 to the topsurface 160 of the heat sink module 100 can be about 0.36 inches, and aheight measured from the bottom surface 135 to the highest surface ofthe angled inlet and outlet ports (105, 110) can be about 0.42 inches.As shown in FIGS. 5, 6, 56, and 57, free space can be limited on amotherboard 405 and in a server 400, and experimental installations haveshown that angled inlet and outlet ports (105, 110) and compact externaldimensions can be very helpful in making heat sink modules 100 fit intight spaces where competing heat sinks are unable to fit.

The heat sink module 100 can include an inlet port 105 that is fluidlyconnected to the inlet chamber 145 by an inlet passage 165. The heatsink module 100 can include a bottom plane 19 associated with the bottomsurface 135, as shown in FIG. 26. The inlet port 105 can be defined by acentral axis 23. The central axis 23 of the inlet port 105 can benon-parallel and non-perpendicular to the bottom plane 19 of the heatsink module 100. For instance, the central axis 23 of the inlet port 105can define an angle of about 10-80, 20-70, 30-60, or 40-50 degrees withrespect to the bottom plane 19 of the heat sink module 100.

The heat sink module 100 can include an outlet port 110 that is fluidlyconnected to the outlet chamber 150 by an outlet passage 166. The outletport 110 can be defined by a central axis 24, as shown in FIG. 29. Thecentral axis 24 of the outlet port 110 can be non-parallel andnon-perpendicular to the bottom plane 19 of the heat sink module 100.For instance, the central axis 24 of the outlet port 110 can define anangle of about 10-80, 20-70, 30-60, or 40-50 degrees with respect to thebottom plane 19 of the heat sink module 100.

Insertable Orifice Plate

In some instances, the heat sink module 100 can include two or morecomponents that are assembled to construct the heat sink module. Sincethe plurality of orifices 155 disposed in the dividing member 195 can bethe most intricate and costly portion of the heat sink module 100 tomanufacture (due to the relatively small diameters of the orifices 155requiring a tighter tolerance manufacturing process than the rest of themodule), it may be desirable to manufacture an orifice plate 198 (e.g.that includes a dividing member 195 and a plurality of orifices 155)separately from the rest of the heat sink module (i.e. the module body104) and subsequently assemble the module body 104 and the orifice plate198. FIG. 65 shows an insertable orifice plate 198 attached to a modulebody 104 to form heat sink module 100.

In some examples, the orifice plate 198 can be manufactured by a firstmanufacturing method and the module body 104 can be manufactured by asecond manufacturing method where the second manufacturing method is,for example, a lower cost and/or lower precision manufacturing methodthan the first manufacturing method. In some examples, the orifice plate198 can be manufactured using a 3-D printing process, and the modulebody 104 can be manufactured by an injection molding process. In otherexamples, the orifice plate 198 can be manufactured by an injectionmolding process, a casting process, or a machining or drilling process,and the module body 104 can be manufactured by any other suitableprocess.

FIG. 65 shows a heat sink module 100 with a module body 104 and aninsertable orifice plate 198 installed therein. The insertable orificeplate 198 can be attached to the heat sink module 100 by any suitablemethod of assembly (e.g. fasteners, press fit, or snap fit). As shown inFIG. 65, the insertable orifice plate 198 can be pressed into the body104 of the heat sink module 100 and can include a sealing member 126that is configured to form a liquid-tight seal between the inlet chamber145 and the outlet chamber 150. In some examples, the insertable orificeplate 198 can be removable, and in other examples the insertable orificeplate 198 may not be easily removable once installed in the body of theheat sink module 100. The plurality of orifice 155 in the orifice plate198 can be optimized to cool a certain device, such as a certain brandand model of microprocessor 415 having a particular non-uniform heatdistribution. When the microprocessor 415, motherboard 405, or entireserver 400 is upgraded to a newer model, a first insertable orificeplate 198 in the heat sink module 100 can be replaced by a secondinsertable orifice plate 198 that has been optimized to cool the newermodel processor that will replace the older one. Consequently, insteadof needing to replace the entire heat sink module 100, only theinsertable orifice plate 198 needs to be replaced to ensure adequatecooling of the newer model processor. This approach can significantlyreduce costs associated with upgrading servers 400 in data centers 425.It can also significantly reduce the cost of optimizing the coolingapparatus 1 when replacing servers 400 in a datacenter 425, since theoriginal cooling apparatus 1, including the pump 20, manifolds (210,215), heat exchangers 40, flexible tubing 225, and fittings 235, cancontinue to be used.

A heat sink module 100 can be configured to cool a heat source, such asa surface 12 of a heat source. The heat sink module 100 can include aninlet chamber 145 formed within the heat sink module. The heat sinkmodule 100 can include an insertable orifice plate 198 and a module body104, as shown in FIG. 65, where the insertable orifice plate isconfigured to attach within the module body 104. The insertable orificeplate 198 can separate the inlet chamber 145 from an outlet chamber 150.The insertable orifice plate 198 can include a first plurality oforifices 155 passing from a top side of the insertable orifice plate 198to a bottom side of the insertable orifice plate 198. The firstplurality of orifices 155 can be configured to deliver a plurality ofjet streams 16 of coolant 50 into the outlet chamber 150 whenpressurized coolant 54 is provided to the inlet chamber 145 of the heatsink module 100. The outlet chamber 150 can have an open portionproximate a bottom surface of the heat sink module 100, and the openportion can be configured to be enclosed by a surface 12 of a heatsource when the heat sink module is installed on the surface of the heatsource. In this example, the first plurality of orifices 155 can have anaverage diameter of about 0.001-0.020, 0.001-0.2, 0.001-0.150,0.001-0.120, 0.001-0.005, or 0.030-0.050 in. The insertable orificeplate 198 can have a thickness of about 0.005-0.25, 0.020-0.1,0.025-0.08, 0.025-0.075, 0.040-0.070, 0.1-0.25, or 0.040-0.070 in.

Jet Height

The heat sink module 100 can have a bottom plane 19 associated with thebottom surface 135 of the heat sink module, as shown in FIG. 26. Thedistance between the bottom plane 19 of the heat sink module and thebottom side of the insertable orifice plate 198 (i.e. where orifice 155outlets are located) defines a “jet height” 18, which can be animportant factor affecting heat transfer rates attainable from thesurface to be cooled 12 in response to impinging jets 16 of coolant 50being delivered from the plurality of orifices 155. In some examples,the distance between the orifice 155 outlets and the surface to becooled 12 can be about 0.01-0.75, 0.05-0.5, 0.05-0.25, 0.020-0.25,0.03-0.125, 0.04-0.08, or about 0.050 in. In some examples, the jetheight 18 can define the height of the outlet chamber 150 of the heatsink module 100.

As shown in FIG. 26, the outlet chamber 150 can have a tapered profilethat permits for expansion of the coolant 50 as the coolant flowstowards the outlet port 110 and as the quality (x) of the coolantincreases in response to vapor formation proximate the surface to becooled 12. To provide this tapered volume, the bottom surface of thedividing member may be arranged at an angle with respect to the surfaceto be cooled. Consequently, a jet height 18 of a first orifice 155located near a front side of the heat sink module 100 may be less than ajet height 18 of a second orifice 155 located near a rear side of theheat sink module. In these examples, a non-uniform jet height 18 may bedefined as falling within a suitable range, such as about 0.01-0.75,0.05-0.5, 0.05-0.25, 0.020-0.25, 0.03-0.125, or 0.04-0.08 in. In otherexamples, an average jet height can be calculated based on thenon-uniform jet height values, and the average jet height can be about0.01-0.75, 0.05-0.5, 0.05-0.25, 0.020-0.25, 0.03-0.125, or 0.04-0.08 in.

In some examples, the distance between the bottom surface of theinsertable orifice plate 198 (or dividing member 195) and the bottomsurface 135 of the heat sink module 100 can define the jet height 18.The jet height (H) can be selected based on the average diameter (d_(n))of the plurality of orifices 155. The relationship between the jetheight 18 and the average diameter of the plurality of orifices 155 canbe expressed as a ratio (H/d_(n)). Examples of suitable values forH/d_(n) can be about 0.25-30, 0.25-10, 5-20, 15-25, or 20-30 for theheat sink module 100 described herein.

Jet Spacing

The orifices 155 within the heat sink module 100 can have any suitableconfiguration forming an array 76. FIGS. 62( a), (b), and (c) showconfigurations of orifices 155 having a rectangular jet array, ahexagonal jet array, and a circular jet array, respectively. Spacing (S)of the orifices 155 can be selected based on the average diameter(d_(n)) of the plurality of orifices 155. As shown in FIG. 62( b), for ahexagonal jet array 76, spacing between jets from left to right (i.e. ina streamwise direction for oblique jet impingement as shown in FIG. 32)is identified as S_(col), and spacing between jets from top to bottom(i.e. cross-stream direction for oblique impingement as shown in FIG.32) is identified as S_(row). Where S_(col) is set equal to S, andS_(row) is set equal to (2_(col)/√3), a relationship between jet spacingS and the average diameter of the plurality of orifices 155 can beexpressed as S/d_(n). Suitable values for S/d_(n) can be about 1.8-330,1.8-50, 25-125, 100-200, 150-250, 200-300, or 275-330 for therectangular, hexagonal, and circular jet arrays 76 shown in FIGS. 62(a), (b), and (c), respectively.

Jet Stream Momentum Flux

In some examples, coolant pressure, coolant temperature, coolant mass,and/or orifice diameter can be selected to provide a jet stream 16 withsufficient momentum flux to penetrate through the coolant 50 in theoutlet chamber 150 and to impinge the surface to be cooled 12, as shownin FIG. 26. By impinging the surface to be cooled 12, the jet stream 16can disrupt vapor bubbles or pockets forming on the surface to be cooled12, thereby increasing the length of the three-phase contact line 58(see, e.g. FIG. 63) and thereby increasing the heat transfer rate fromthe surface to be cooled 12 to the coolant 50 and delaying the onset ofcritical heat flux.

To provide desirable heat transfer from the surface to be cooled 12,experimental testing demonstrated that jet stream 16 momentum fluxshould be at least 23 kg/m-s² when using R245fa as the coolant 50 andshould be at least 24 kg/m-s² when using HFE-7000 as the coolant 50.Suitable values of jet stream 16 momentum flux from each orifice include24-220, 98-390, 220-611, 390-880, 611-1200, 880-1566, and greater than1566 kg/m-s². Although a high jet stream 16 momentum flux can bedesirable to increase heat transfer rates, reducing the jet streammomentum flux can be desirable to reduce power consumption by the pump20, and thereby increase efficiency of the cooling apparatus 1.Experimental tests showed that jet stream 16 momentum fluxes of about95-880, 220-615, and about 390 kg/m-s² produced a desirable balance ofhigh heat transfer rates and low power consumption by the pump 20.

Internal Threads on Inlet and Outlet Ports

In some examples, corrugated, flexible tubing 225 can be used to fluidlyconnect heat sink modules 100 to the cooling apparatus. The corrugated,flexible tubing 225 can include spiral corrugations extending along thelength of the tubing 225, similar to course threads on a screw. Tofacilitate fast connection of a section of flexible tubing 225 to theheat sink module 100, corresponding corrugation-mating features can beprovided on the interior surfaces of the inlet and outlet ports (105,110) of the heat sink module. The corresponding corrugation-matingfeatures can be molded into the inlet and outlet ports (105, 110)thereby serving as internal threads. As a result, fluidly connecting asection of flexible corrugated tubing 225 to a port (105 or 110) of theheat sink module 100 can be as simple as threading the section of tubing225 into the port. In some examples the diameter of the port (105, 110)can taper inward, thereby ensuring a liquid-tight fit as the section oftubing 225 is threaded into the port. To further ensure a liquid-tightseal, a thread sealant, such as a Teflon tape or a spreadable threadsealant can be provided between the interior surface of the port (105,110) and the outer surface of the section of flexible tubing 225. Inother examples, an adhesive, such as epoxy, can be provided between theinterior surface of the port (105, 110) and the outer surface of thesection of flexible tubing 225 to further ensure a liquid-tight seal andto prevent inadvertent disconnection of the section of tubing from theport.

Non-Threaded Connections

To speed installation of the heat sink module 100, for example, into aserver 400, the threaded ports 105, 110 of the heat sink module 100 canbe replaced with non-threaded ports. In one example, the non-threadedports can be quick-connect ports are configured to mate with acorresponding quick connect coupler, such as a corresponding quickconnect coupler attached to a section of flexible tubing 225. In thisexample, the quick-connect features of the quick-connect ports can bemanufactured using a 3D printer. In another example, the non-threadedports can be configured to receive smooth, flexible tubing 225 within ininner diameter of each port or over an outer diameter of each port. Anepoxy or other suitable adhesive can be used to bond the flexible tubing225 to the port (105, 110) of the heat sink module 100 to form aconnector-less fluid coupling.

Leakproof Coating

The heat sink module 100 can be manufactured from a plastic materialthrough, for example, an injection molding process or an additivemanufacturing process. Depending of the properties of the plasticmaterial used to manufacture the heat sink module 100, and the type ofcoolant 50 used with the cooling apparatus 1 (and the molecular size ofthe coolant), leakage of coolant through the walls of the heat sinkmodule 100 may occur. To avoid leakage, the heat sink module 100 can becoated with a leakproof coating. In some examples, the leakproof coatingcan be a metalized coating, such as a nickel coating deposited on anouter surface of the heat sink module 100 or along the inner surfaces ofthe heat sink module (e.g. inner surfaces of the inlet and outlet ports,inlet and outlet passages, and inlet and outlet chambers). The leakproofcoating can be made of a suitable material and can have a suitablethickness to ensure that coolant does not migrate through the walls ofthe heat sink module 100 and into the environment. The leakproof coatingcan be applied to surfaces of the heat sink module 100 by any suitableapplication method, such as arc or flame spray coating, electroplating,physical vapor deposition, or chemical vapor deposition.

Internal Bypass in Heat Sink Module

To promote condensing of two-phase bubbly flow upstream of the reservoir200, and thereby reduce the likelihood of vapor being drawn into thepump 20 from the reservoir, the heat sink module 100 can include aninternal bypass that routes a portion of the coolant 50 flow deliveredto the inlet port 105 of the module around the heated surface 12. Theinternal bypass can be formed within the heat sink module 100. Forinstance, the internal bypass can be a, injection molded, cast, or 3Dprinted internal bypass formed within the heat sink module 100 andconfigured to transport coolant from the inlet port 105 to the outletport 110 without bringing the fluid in contact with the surface to becooled 12. The coolant that flows through the internal bypass can remainsingle-phase liquid coolant that is below the saturation temperature ofthe coolant. Near the outlet port 110 of the heat sink module 100, thesingle-phase liquid coolant that is diverted through the internal bypasscan be mixed with two-phase bubbly flow (i.e. two-phase bubbly flowgenerated by jet stream impingement against the surface to be cooled 12)that was not diverted. Mixing of the single-phase liquid coolant withthe two-phase bubbly flow can result in condensation and collapse ofvapor bubbles 275 within the mixed flow 50, thereby reducing the voidfraction of the coolant 50 flow delivered to the reservoir 200 and, inturn, reducing the likelihood of vapor bubbles being delivered to thepump 20.

In some examples, as shown in FIG. 12E, the internal bypass 65 in theheat sink module can include a pressure regulator 60. The pressureregulator 60 can be disposed at least partially within the internalbypass 65 and can serve to restrict flow through the internal bypass 65,thereby controlling the proportion of coolant flow through the internalbypass, and as a result, the proportion of coolant flow through theplurality of orifices 155 along a standard flow path 66 through the heatsink module. The internal pressure regulator 60 can be an active orpassive regulator. In some examples, the pressure regulator can be athermostatic valve that increases flow through the internal bypass 65 asthe temperature of the coolant increases or decreases. In otherexamples, the pressure regulator 60 can be computer controlled pressureregulator where flow is adjusted based on a temperature and/or apressure of the coolant upstream or downstream of the heat sink module100. In other examples, the pressure regulator 60 can be a simple flowconstriction (e.g. a physical neck) in the internal bypass thateffectively restricts flow by providing flow resistance.

Flow-Guiding Lip

The heat sink module 100 can include a flow-guiding lip 162, as shown inFIG. 30. The flow-guiding lip 162 can guide a directional flow 51 ofcoolant from the outlet chamber 150 to the outlet passage 166.Preferably, the flow-guiding lip 162 can have an angle of less thanabout 45 or less than about 30 degrees with respect to the surface to becooled 12 to avoid creating a flow restriction or stagnation regionproximate the exit of the outlet chamber 150. By avoiding formation of astagnation region, the flow-guiding lip 162 can prevent onset ofcritical heat flux near the exit of the outlet chamber 150.

Heat Sink Assembly

FIG. 7 shows a heat sink assembly including a heat sink module 100fluidly connected to two sections of flexible tubing 225. The heat sinkmodule 100 has an inlet port 105 and an outlet port 110. One end of thefirst section of flexible tubing 225 is fluidly connected to the inletport 105 by a first connector 120, and one end of the second section offlexible tubing 225 is fluidly connected to the outlet port 110 by asecond connector 120. In some examples, the connectors 120 can beliquid-tight fittings, such as compression fittings. The heat sinkassembly can be used to cool any heat generating surface associated witha device, such as an electrical or mechanical device.

Series-Connected Heat Sink Modules

FIG. 14A shows a schematic of a cooling apparatus 1 having three heatsink modules 100 arranged in a series configuration on three surfaces tobe cooled 12. As shown by way of example in FIG. 15, the three heat sinkmodules 100 can be fluidly connected with tubing, such as flexibletubing 225. The three surfaces to be cooled 12 can be three separatesurfaces to be cooled or can be three different locations on the samesurface to be cooled 12.

FIG. 15 shows a portion of a primary cooling loop 300 of a coolingapparatus 1 where the cooling loop 300 includes three series-connectedheat sink modules 100 mounted on three heat-providing surfaces 12 (see,e.g. FIG. 14A). The heat sink module 100 can be connected by sections offlexible tubing 225. A single-phase liquid coolant 50 can be provided toa first heat sink module 100 by a section of tubing 225-0, and due toheat transfer occurring within the first heat sink module 100-1 (i.e.heat being transferred from the first heat-generating surface 12 to theflow of coolant), two-phase bubbly flow can be generated and transportedin a first section of flexible tubing 225-1 extending from the firstheat sink module 100-1 to the second heat sink module 100-2. Thetwo-phase bubbly flow contains a plurality of bubbles 275 having a firstnumber density. Due to heat transfer occurring within the second heatsink module 100-2 (i.e. heat being transferred from the secondheat-generating surface 12 to the flow of coolant), higher quality (x)two-phase bubbly flow can be generated and transported from the secondmodule 100-2 to the third heat sink module 100-3 through a secondsection of flexible tubing 225-2. In the second section of flexibletubing 225, the two-phase bubbly flow contains a plurality of bubbles275 having a second number density, where the second number density ishigher than the first number density. Due to heat transfer occurringwithin the third heat sink module 100 (i.e. heat being transferred fromthe third heat-generating surface 12 to the flow of coolant), evenhigher quality (x) two-phase bubbly flow can be generated andtransported out of the third heat sink module 100-3 through a thirdsection of tubing 225-3. In the third section of tubing 225-3, thetwo-phase bubbly flow contains a plurality of bubbles 275 having a thirdnumber density, where the third number density is higher than the secondnumber density.

FIG. 14B shows a representation of coolant flowing through three heatsink modules (100-1, 100-2, 100-3) connected in series by four lengthsof tubing (225-1, 225-2, 225-3, 225-4), similar to the configurationsshown in FIGS. 14A and 15. FIG. 14B also shows corresponding plots ofsaturation temperature (T_(sat)), liquid coolant temperature(T_(liquid)), pressure (P), and quality (x) of the coolant versusdistance along a flow path through the series-connected heat sinkmodules. In the example, a flow 51 of single-phase liquid coolant 50enters the first heat sink module 100-1 through a first section oftubing 225-1 at a temperature that is slightly below the saturationtemperature of the liquid coolant 50. Within the first heat sink module100-1, the single-phase liquid coolant 50 is projected against a firstsurface to be cooled 12-1 by way of a plurality of jet streams 16 ofcoolant. A first portion of the liquid coolant 50 changes phase andbecomes vapor bubbles 275 dispersed in the liquid coolant 50, therebyproducing two-phase bubbly flow having a first quality (x₁). Thetwo-phase bubbly flow having the first quality is transported from thefirst heat sink module 100-1 to a second heat sink module 100-2 by asecond section of tubing 225-2. Within the second heat sink module100-2, the two-phase bubbly flow having a first quality is projectedagainst a second surface to be cooled 12-2 by way of a plurality of jetstreams 16 of coolant. A second portion of the liquid coolant 50 changesphase and becomes vapor bubbles 275 dispersed in the liquid coolant 50,thereby producing two-phase bubbly flow having a second quality (x₂)that is greater than the first quality (i.e. x₂>x₁). The two-phasebubbly flow having the second quality is transported from the secondheat sink module 100-2 to a third heat sink module 100-3 by a thirdsection of tubing 225-3. Within the third heat sink module 100-3, thetwo-phase bubbly flow having a second quality is projected against athird surface to be cooled 12-3 by way of a plurality of jet streams 16of coolant. A third portion of the liquid coolant 50 changes phase andbecomes vapor bubbles 275 dispersed in the liquid coolant 50, therebyproducing two-phase bubbly flow having a third quality (x₃) that isgreater than the second quality (i.e. x₃>x₂). As shown in FIG. 14B,along the distance of the flow path, quality of the coolant increases,pressure decreases, liquid coolant temperature (T_(liquid)) decreases,and T_(sat) decreases through successive series-connected heat sinkmodules.

Through each successive heat sink module 100, the flow of coolant 51experiences a pressure drop, as shown in FIG. 14B. In some examples, thepressure drop across each heat sink module 100 can be about 0.5-5.0,0.5-3, 1-3, or 1.5 psi. The pressure drop across each heat sink module100 causes a corresponding decrease in saturation temperature (Tsat) ofthe coolant. Accordingly, the temperature of the liquid coolantcomponent of the two-phase bubbly flow also decreases in response todecreasing saturation temperature at each pressure drop at each module.Consequently, the third heat sink module 100-3 receives two-phase bubblyflow containing liquid coolant 50 that is cooler than liquid coolant 50in the two-phase bubbly flow received by the second heat sink module100-2. As a result of this phenomenon, the cooling apparatus 1 is ableto maintain the third surface to be cooled 12-3 at a temperature belowthe temperature of a second surface to be cooled 12-2 when the secondand third surfaces to be cooled have equal heat fluxes. Because of thisbehavior, additional series connected heat sink modules 100 can be addedto the series configuration. In some examples four, six, or eight ormore heat sink modules 100 can be connected in series with eachsuccessive module receiving two-phase bubbly flow containing liquidcoolant 50 that is slightly cooler than the liquid coolant received bythe previous module connected in series. The only limitation on thenumber of series-connected modules that can be used a threshold quality(x) value, which if exceeded, could result in unstable flow. However, ifthe cooling system 1 is on the verge of exceeding the threshold quality(x) value, the coolant flow rate can be increased to decrease the flowquality.

HFE-7000 can be used as coolant 50 in the cooling apparatus 1. HFE-7000has a boiling temperature of about 34 degrees Celsius at a pressure of 1atm. In the example shown in FIGS. 14A, 14B, and 15, HFE-7000 can beintroduced to the series configuration as single-phase liquid coolant ata pressure of about 1 atmosphere and a temperature slightly below 34degrees Celsius. A flow rate of about 0.1-10, 0.2-5, 0.3-2.5, 0.6-1.2,or 0.8-1.1 liters per minute of single-phase coolant can be provided. Asthe coolant flows through the first, second, and third heat sinkmodules, the coolant may experience a total pressure drop of about 5-10,8-12, or 10-15 psi. At each heat sink module, the coolant may experiencea pressure drop of about 0.5-5.0, 0.5-3, 1-3, or 1.5 psi. As shown inFIG. 14B, a drop in saturation temperature accompanies each pressuredrop, and a drop in liquid temperature follows each decrease insaturation temperature. Consequently, the temperature of the liquidcomponent 50 of the two-phase bubbly flow continues to decrease throughthe series connection and exits the third heat sink module 100-3 at atemperature below 34 degrees Celsius, where the temperature depends onpressure and quality of the exiting flow 51. In this example, throughthe first heat sink module 100-1, heat transfer occurs via sensible andlatent heating of the coolant, and through the second and third heatsink modules (100-2, 100-3), heat transfer occurs primarily by latentheating of the coolant.

In competing pumped liquid cooling systems, such as those that usepumped single-phase water as a coolant, the coolant becomesprogressively warmer (due to sensible heating) as it passes through eachsuccessive series-connected heat sink module. For this reason, competingsingle-phase cooling systems typically cannot support more than twoseries connected heat sink modules, because the coolant temperature atthe outlet of the second heat sink module is too hot to properly cool athird heat sink module. Where competing pumped liquid cooling systemsinclude multiple series-connected heat sink modules, the cooling systemis unable to maintain sensitive devices, such as microprocessors, atuniform temperatures, and the last device in series may experiencesub-optimal performance or premature failure in response to operating atelevated temperatures.

FIG. 14C shows a representation of coolant flowing through three heatsink modules (100-1, 100-2, 100-3) connected in series by lengths oftubing (225-1, 225-2, 225-3, 225-4), similar to FIG. 14B, except thatthe coolant does not reach its saturation temperature until the secondheat sink module 100-2. Consequently, single-phase liquid coolant 50flows through the first heat sink module 100-1 (where no vapor isformed) and travels to the second heat-sink module 100-2 at an elevatedtemperature due to sensible heating. Within the second heat sink-module100-2, a pressure drop occurs, as does a corresponding drop insaturation temperature. Heat transfer from the second surface to becooled 12-2 to the single-phase liquid coolant 50 causes a portion ofthe coolant to vaporize. Consequently, heat transfer within the secondheat sink module 100-2 can be a combination of latent heating andsensible heating. Two-phase bubbly flow can then be transported from thesecond heat sink module 100-2 to the third heat sink module 100-3 in athird section of tubing 225-3. Within the third heat sink module 100-3,since the temperature of the liquid component 50 of the coolant is at ornearly at its saturation temperature, heat transfer may occur primarilyby latent heating, as evidenced by an increase in quality (x), as shownin FIG. 14C.

The method shown in FIG. 14C can be less efficient than the method shownin FIG. 14B, since it does not employ latent heating within the firstheat sink module 100-1 and may therefore require higher flow rates andmore pump work to adequately cool the first surface to be cooled 12-1.However, the method in FIG. 14C can be easier to achieve and maintain,since the temperature of the incoming single-phase liquid coolant 50does not need to be controlled as carefully as the method shown in FIG.14B (e.g. with respect to providing a temperature that is slightly belowthe saturation temperature). In some examples, an operating method canalternate between the methods shown in FIGS. 14B and 14C depending onthe temperature of the incoming single-phase coolant 50. For instance,where the system is undergoing transient operation, due to changing heatloads or changing chiller loop conditions, the operating method canalternate from the method shown in FIG. 14B to the method shown in FIG.14C for safety until the transient condition subsides. Once thetransient condition is over, the microcontroller 850 of the coolingapparatus 1 can begin to ramp up the temperature of the incomingsingle-phase liquid coolant 50 to a temperature that is slightly belowits saturation temperature. By employing this control strategy, thecooling system 1 can avoid instabilities caused by excess vaporformation during transient conditions. One strategy for decreasing thetemperature of the incoming single-phase liquid coolant 50 can includeincreasing the flow rate through the heat exchanger 40 to reduce thetemperature of the coolant in the reservoir 200, which is then deliveredto the series-configuration by the pump 20.

In one example, a method of cooling two or more processors 415 of aserver 400 can include providing a cooling apparatus 1 having two ormore series-connected heat sink modules 100, as shown in FIG. 15, and inFIGS. 14A, 14B, 14C, 16, 74, and 78-80. The method can include providinga flow 51 of dielectric single-phase liquid coolant 50 to an inlet port105 of a first heat sink module 100-1 in thermal communication with afirst processor 415 of a server 400. A first amount of heat can betransferred from the first processor (12, 415) to the dielectricsingle-phase liquid coolant 50 resulting in vaporization of a portion ofthe dielectric single-phase liquid coolant thereby changing the flow ofdielectric single-phase liquid coolant to two-phase bubbly flow made ofdielectric liquid coolant with dielectric vapor coolant dispersed asbubbles 275 in the dielectric liquid coolant 50. Consequently, heat fromthe processor 415 is absorbed to the coolant across the coolant's heatof vaporization, which is a far more efficient method for absorbingheat. For a dielectric coolant, such as NOVEC 7000, the latent heat ofvaporization is 142,000 J/kg, whereas the specific heat for sensiblewarming the coolant is only 1,300 J/(kg-K). Therefore, by vaporizing aportion of the liquid coolant 50 within the heat sink module 100-1, thatportion of coolant is able to absorb significantly more heat (on anorder of 100 times more heat) from the processor (12, 415) than if theliquid coolant 50 were simply warmed inside the heat sink module 100-1by one or two degrees without experiencing any vaporization. Thetwo-phase bubbly flow that is formed within the first heat sink module100-1 can have a first quality (x₁). The method can include transportingthe two-phase bubbly flow from an outlet port 110 of the first heat sinkmodule 100 to an inlet port 105 of a second heat sink module 100-2connected in series with the first heat sink module 100-1. The secondheat sink module 100-2 can be in thermal communication with a secondprocessor (12, 415) of the server 400. A second amount of heat can betransferred from the second processor (12, 415) to the two-phase bubblyflow resulting in vaporization of a portion of the dielectric liquidcoolant within the two-phase bubbly flow thereby resulting in a changefrom the first quality (x₁) to a second quality (x₂). The second quality(x₂) can be greater than the first quality (x₁). The first quality (x₁)can be about 0-0.1, 0.05-0.15, 0.1-0.2, 0.15-0.25, 0.2-0.3, 0.25-0.35,0.3-0.4, 0.35-0.45, 0.4-0.5, 0.45-0.55, and the second quality (x₂) canbe about 0-0.1, 0.05-0.15, 0.1-0.2, 0.15-0.25, 0.2-0.3, 0.25-0.35,0.3-0.4, or 0.4-0.45 greater than the first quality.

Energy from the first amount of heat and the second amount of heat canbe stored, at least in part, as latent heat in the two-phase bubbly flowand transported out of the server through a flexible cooling line. Theliquid coolant in the two-phase bubbly flow 51 that is transportedbetween the first heat sink module 100-1 and the second heat sink module100-2 can have a temperature at or slightly below its saturationtemperature. The pressure of the two-phase bubbly flow can be about0.5-5.0, 0.5-3, or 1-3 psi less than the predetermined pressure of theflow of dielectric single-phase liquid coolant provided to the inletport of the first heat sink module, as shown in the pressure versusdistance plots of FIGS. 14B and 14C.

A saturation temperature of the two-phase flow 51 having the secondquality (x₂) can be less than a saturation temperature of the two-phaseflow having the first quality (x₁), thereby allowing the secondprocessor (12, 415) to remain at a slightly lower temperature than thefirst processor (12, 415) when a first heat flux from the firstprocessor is approximately equal to a second heat flux from the secondprocessor, as shown in the temperature versus distance plots of FIGS.14B and 14C. Providing the flow 51 of dielectric single-phase liquidcoolant to the inlet port 105 of the first heat sink module 100-1 caninclude providing a flow rate of about 0.1-10, 0.2-5, 0.3-2.5, 0.6-1.2,or 0.8-1.1 liters per minute of dielectric single-phase liquid coolantto the first inlet port of the first heat sink module. The flow ofsingle-phase liquid coolant can have a boiling point of about 15-35,20-45, 30-55, or 40-65 degrees C. determined at a pressure of 1 atm. Thedielectric coolant can be a hydrofluoroether, a hydrofluorocarbon, or acombination thereof. Providing the flow of dielectric single-phaseliquid coolant to the first heat sink module 100-1 can include providingthe flow 51 of dielectric single-phase liquid coolant at a predeterminedtemperature and a predetermined pressure, where the predeterminedtemperature is slightly below the saturation temperature (T_(sat)) ofthe flow of dielectric single-phase liquid coolant at the predeterminedpressure. The predetermined temperature can about 0.5-20, 0.5-15,0.5-10, 0.5-7, 0.5-5, 0.5-3, 0.5-1, 1-20, 1-15, 1-10, 1-7, 1-5, 1-3,3-20, 3-15, 3-10, 3-7, 3-5, 5-20, 5-15, 5-10, 5-7, 7-20, 7-15, 7-10,10-20, 10-15, or 15-20 degrees C. below the saturation temperature(T_(sat)) of the flow of dielectric single-phase liquid coolant at thepredetermined pressure.

The method can include providing a pressure differential of about0.5-5.0, 0.5-3, or 1-3 psi between the inlet port 105 of the first heatsink module 100-1 and the outlet port 110 of the first heat sink module.The pressure differential can be suitable to promote the flow 51 ofcoolant to advance from the inlet port 105 of the first heat sink module100-1 to the outlet port 110 of the first heat sink module. The methodcan include transporting the two-phase bubbly flow 51 from an outletport 110 of the second heat sink module 100-2 to an inlet port of athird heat sink module 100-3 connected in series with the first andsecond heat sink modules. The third heat sink module 100-3 can be inthermal communication with a third processor (12, 415) of the server400. A third amount of heat can be transferred from the third processor(12, 415) to the two-phase bubbly flow 51 resulting in vaporization of aportion of the dielectric liquid coolant 50 within the two-phase bubblyflow thereby resulting in a change from the second quality (x₂) to athird quality (x₃). The third quality (x₃) can be greater than thesecond quality (x₂).

In another example, a method of cooling two or more processors 415 in anelectronic device can include providing a cooling apparatus 1 with twoor more fluidly connected heat sink modules arranged in a seriesconfiguration, as shown in FIG. 15. The method can include providing aflow 51 of dielectric single-phase liquid coolant to a first heat sinkmodule 100-1. The first heat sink module 100-1 can include a firstthermally conductive base member 430 in thermal communication with afirst processor 415 in an electronic device. The dielectric single-phaseliquid coolant can have a predetermined pressure and a predeterminedtemperature at a first inlet 105 of the first heat sink module 100-1.The predetermined temperature can be slightly below a saturationtemperature (T_(sat)) of the dielectric single-phase liquid coolant atthe predetermined pressure. The method can include projecting the flowof dielectric single-phase liquid coolant against the thermallyconductive member (e.g. in the form of impinging jet streams 16 ofcoolant) within the first heat sink module 100-1. A first amount of heatcan be transferred from the processor 415 through the thermallyconductive base member 430 and to the flow 51 of dielectric single-phaseliquid coolant thereby inducing phase change in a portion of the flow ofdielectric single-phase liquid coolant and thereby changing the flow ofdielectric single-phase liquid coolant to two-phase bubbly flow having adielectric liquid coolant 50 and a plurality of vapor bubbles 275dispersed in the dielectric liquid coolant. Consequently, heat from theprocessor 415 is absorbed to the coolant 50 across the coolant's heat ofvaporization, which is a far more efficient method for absorbing heat.For a dielectric coolant, such as NOVEC 7000, the latent heat ofvaporization is 142,000 J/kg, whereas the specific heat for sensiblewarming the coolant is only 1,300 J/(kg-K). Therefore, by vaporizing aportion of the liquid coolant 50 within the heat sink module 100-1, thatportion of coolant is able to absorb significantly more heat (on anorder of 100 times more heat) from the processor 415 than if the liquidcoolant 50 were simply warmed inside the heat sink module 100-1 by oneor two degrees without experiencing any vaporization. The plurality ofvapor bubbles 275 in the two-phase bubbly flow can have a first numberdensity.

The method can include providing a second heat sink module 100-2 havinga second thermally conductive base member 430 in thermal communicationwith a second processor 415. The second heat sink module 100-2 can havea second inlet 105. The method can include providing a first section oftubing 225-1 having a first end connected to the first outlet 110 of thefirst heat sink module 100-1 and a second end connected to the secondinlet 105 of the second heat sink module 100-2. The first section oftubing 225-1 can transport the two-phase bubbly flow 51 having the firstnumber density from the first outlet 105 of the first heat sink module100-1 to the second inlet 110 of the second heat sink module 100-2. Themethod can include projecting the two-phase bubbly flow having the firstnumber density against the second thermally conductive base member (e.g.in the form of impinging jet streams 16 of coolant) within the secondheat sink module 100-2. A second amount of heat can be transferred fromthe second processor 415 through the second thermally conductive basemember 430 and to the two-phase bubbly flow having a first numberdensity thereby changing two-phase bubbly flow having a first numberdensity to a two-phase bubbly flow having a second number densitygreater than the first number density.

A saturation temperature (T_(sat)) and pressure of the two-phase flowhaving a second number density can be less than a saturation temperatureand pressure of the two-phase flow having a first number density,thereby allowing the second processor 415 to be maintained at a slightlylower temperature than the first processor when a first heat flux fromthe first processor is approximately equal to a second heat flux fromthe second processor, as shown in the temperature versus distance plotsof FIGS. 14 b and 14C. The predetermined temperature of the flow 51 ofdielectric single-phase liquid coolant at the first inlet 105 of thefirst heat sink module 100-1 can be about 0.5-20, 0.5-15, 0.5-10, 0.5-7,0.5-5, 0.5-3, 0.5-1, 1-20, 1-15, 1-10, 1-7, 1-5, 1-3, 3-20, 3-15, 3-10,3-7, 3-5, 5-20, 5-15, 5-10, 5-7, 7-20, 7-15, 7-10, 10-20, 10-15, or15-20 degrees C. below the theoretical saturation temperature (T_(sat))of the flow of dielectric single-phase liquid coolant at thepredetermined pressure of the flow of dielectric single-phase liquidcoolant at the first inlet 105 of the first heat sink module 100-1.Providing the flow 51 of dielectric single-phase liquid coolant to theinlet of the first heat sink module includes providing a flow rate ofabout 0.1-10, 0.2-5, 0.3-2.5, 0.6-1.2, or 0.8-1.1 liters per minute ofsingle-phase liquid coolant to the first inlet 105 of the first heatsink module 100-1. The liquid in the two-phase bubbly flow 51 beingtransported between the first heat sink module 100-1 and the second heatsink module 100-2 can have a temperature at or slightly below itssaturation temperature (T_(sat)), where a pressure of the two-phasebubbly flow having a first number density can be about 0.5-5.0, 0.5-3,or 1-3 psi less than the predetermined pressure of the flow ofsingle-phase liquid coolant provided to the first heat sink module100-1.

The electronic device can be a server 400, a personal computer, a tabletcomputer, a power electronics device, a smartphone, a network switch, atelecommunications system, an automotive electronic control unit, abattery management device, a progressive gaming device for a casino, ahigh performance computing (HPC) system, a server-based gaming device,an avionics system, or a home automation control unit. The firstprocessor can be a central processing unit (CPU) or a graphicsprocessing unit (GPU). Likewise, the second processor can be a CPU or aGPU.

In yet another example, a method of cooling three or more processors 415on a motherboard 405 can employ a two-phase cooling apparatus havingthree or more fluidly-connected and series-connected heat sink modules,as shown in FIG. 15. The method can include providing a flow 51 ofdielectric single-phase liquid coolant to an inlet port 105 of a firstheat sink module 100-1 mounted on a first thermally conductive basemember 430. The first thermally conductive base member 430 can bemounted on a first processor 415 on a motherboard 405, as shown in FIGS.84-89. Heat can be transferred from the first processor 415 through thefirst thermally conductive base member 430 and to the flow of dielectricsingle-phase liquid coolant resulting in boiling of a first portion ofthe dielectric single-phase liquid coolant, thereby changing the flow ofdielectric single-phase liquid coolant to two-phase bubbly flow having afirst quality, as shown in FIG. 99. Consequently, heat from the firstprocessor 415 is absorbed to the coolant across the coolant's heat ofvaporization, which is a far more efficient method for absorbing heatthan sensible heating. For a dielectric coolant, such as NOVEC 7000, thelatent heat of vaporization is 142,000 J/kg, whereas the specific heatfor sensible warming the coolant is only 1,300 J/(kg-K). Therefore, byvaporizing a portion of the liquid coolant 50 within the heat sinkmodule 100-1, that portion of coolant is able to absorb significantlymore heat (on an order of 100 times more heat) from the processor 415than if the liquid coolant 50 were simply warmed inside the heat sinkmodule 100-1 by one or two degrees without experiencing anyvaporization.

The method can include transporting the two-phase bubbly flow 51 from anoutlet port of 110 the first heat sink module 100-1 to an inlet port 105of a second heat sink module 100-2 through a first section of flexibletubing 225-1, as shown in FIG. 99. The second heat sink module 100-2 canbe mounted on a second thermally conductive base member 430. The secondthermally conductive base member 430 can be mounted on a secondprocessor 415 on the motherboard 405. Heat can be transferred from thesecond processor 415 through the second thermally conductive base member430 and to the two-phase bubbly flow 51 resulting in vaporization of aportion of dielectric liquid coolant 50 within the two-phase bubblyflow, thereby resulting in a change from the first quality (x₁) to asecond quality (x₂), where the second quality is higher than the firstquality. The method can include transporting the two-phase bubbly flow51 from an outlet port 110 of the second heat sink module 100-2 to aninlet port 105 of a third heat sink module 100-3 through a secondsection of flexible tubing 225-2. The third heat sink module 100-3 canbe mounted on a third thermally conductive base member 430. The thirdthermally conductive base member 430 can be mounted on a third processor415 on the motherboard 405. Heat can be transferred from the thirdprocessor 415 through the third thermally conductive base member 430 andto the two-phase bubbly flow 51 resulting in vaporization of a portionof dielectric liquid coolant within the two-phase bubbly flow, therebyresulting in a change from the second quality (x₂) to a third quality(x₃), where the third quality is higher than the second quality. Themotherboard 405 can be associated with a server 400, a personalcomputer, a tablet computer, a power electronics device, a smartphone,an automotive electronic control unit, a battery management device, ahigh performance computing system, a progressive gaming device, aserver-based gaming device, a telecommunications system, an avionicssystem, or a home automation control unit.

In one example, a method of cooling two or more processors 415 of aserver 400 can involve absorbing sensible heat and latent heat incoolant 50 flowing through two or more series-connected heat sinkmodules 100. The method can include providing a flow 51 of subcooledsingle-phase liquid coolant to an inlet 105 of a first heat sink module100-1 in thermal communication with a first processor 415 of a server400, as shown in FIG. 98. The subcooled single-phase liquid coolant canabsorb a first amount of heat from the first processor 415 as sensibleheat. The method can include transporting the flow 51 of subcooledsingle-phase liquid coolant from an outlet 110 of the first heat sinkmodule 100-1 to an inlet 105 of a second heat sink module 100-2 inthermal communication with a second processor 415 of the server 400. Thesubcooled single-phase liquid can absorb a second amount of heat fromthe second processor 415 as sensible heat resulting in the flow ofsubcooled single-phase liquid coolant reaching its saturationtemperature and becoming a flow of saturated single-phase liquidcoolant. The flow of saturated single-phase liquid coolant can absorb athird amount of heat from the second processor as latent heat resultingin vaporization of a first portion of the flow of saturated single-phaseliquid coolant thereby changing the flow of saturated single-phaseliquid coolant to two-phase bubbly flow including saturated liquidcoolant 50 with vapor coolant dispersed as bubbles 275 in the saturatedliquid coolant, as shown in FIG. 98.

The method can include transporting the flow 51 of two-phase bubbly flowcontaining the first amount of heat, the second amount of heat, and thethird amount of heat out of the server through a flexible cooling line303, as shown in FIG. 98. The method can include rejecting the firstamount of heat, the second amount of heat, and the third amount of heatfrom the flow of two-phase bubbly flow by directing the flow oftwo-phase bubbly flow through a heat exchanger 40 fluidly connected toan external heat rejection loop 43. The external heat rejection loop 43can then reject the first, second, and third amounts of heat to achilled water supply or to ambient air outside of a data center facility425 where the server 400 is located.

The method can include projecting the flow 51 of subcooled single-phaseliquid coolant 50, in the form of impinging jet streams 16, against afirst surface to be cooled 12 within the first heat sink module 100-1,as shown in FIGS. 26 and 27. Similarly, the method can includeprojecting the flow 51 of subcooled single-phase liquid coolant 50, inthe form of impinging jet streams 16, against a second surface to becooled 12 within the second heat sink module 100-2.

Providing the flow of subcooled single-phase liquid coolant to the inlet105 of the first heat sink module 100-1 can include providing a flowrate of about 0.1-10, 0.2-5, 0.3-2.5, 0.6-1.2, or 0.8-1.1 liters perminute of subcooled single-phase liquid coolant to the first inlet 105of the first heat sink module 100-1. Providing the flow 51 of subcooledsingle-phase liquid coolant 50 to the inlet 105 of the first heat sinkmodule 100-1 can include providing a subcooled single-phase liquidcoolant with a boiling point of about 15-35, 20-45, 30-55, or 40-65degrees C. determined at a pressure of 1 atm. Providing the flow 51 ofsubcooled single-phase liquid coolant to the inlet 105 of the first heatsink module 100-1 can include providing a dielectric coolant 50including a hydrofluoroether, a hydrofluorocarbon, or a combinationthereof. Providing the flow 51 of subcooled single-phase liquid coolant50 to the first heat sink module 100-1 can include providing a flow 51of subcooled single-phase liquid coolant at a predetermined temperatureand a predetermined pressure. The predetermined temperature can be belowthe saturation temperature of the flow of subcooled single-phase liquidcoolant at the predetermined pressure. The predetermined temperature canbe about 0.5-20, 0.5-15, 0.5-10, 0.5-7, 0.5-5, 0.5-3, 0.5-1, 1-20, 1-15,1-10, 1-7, 1-5, 1-3, 3-20, 3-15, 3-10, 3-7, 3-5, 5-20, 5-15, 5-10, 5-7,7-20, 7-15, 7-10, 10-20, 10-15, or 15-20 degrees C. below the saturationtemperature of the flow of subcooled single-phase liquid coolant at thepredetermined pressure. The method can include providing a pressuredifferential of about 0.5-5.0, 0.5-3, or 1-3 psi between the inlet 105of the first heat sink module 100-1 and the outlet 110 of the first heatsink module. The pressure differential can be suitable to promote theflow 51 of subcooled single-phase liquid coolant to advance from theinlet 105 of the first heat sink module 100-1 to the outlet 110 of thefirst heat sink module.

The method can include transporting the two-phase bubbly flow having afirst quality (x₁) from an outlet 110 of the second heat sink module100-2 to an inlet 105 of a third heat sink module 100-3 connected inseries with the first and second heat sink modules. The third heat sinkmodule 100-3 can be in thermal communication with a third processor 415of the server 400. The two-phase bubbly flow having the first quality(x₁) can absorb a fourth amount of heat from the third processor 415 aslatent heat resulting in vaporization of a second portion of thesaturated single-phase liquid coolant thereby changing the flow fromtwo-phase bubbly flow with a first quality to two-phase bubbly flow witha second quality (x₂) greater than the first quality.

The method can include directing the flow 51 of subcooled single-phaseliquid coolant 50 through one or more series-connected heat sink modulesprior to providing the flow of subcooled single-phase liquid coolant tothe inlet 105 of the first heat sink module 100-1. This arrangement canallow the coolant 50 to absorb sensible heat as it flows through the oneor more heat sink modules 100 before reaching the first heat sink module100-1. The one or more heat sink modules 100 can effectively serve aspreheaters, thereby allowing the cooling apparatus 1 to achievevaporization in subsequent heat sink modules in the series connectionwithout requiring sophisticated temperature control system to deliverthe coolant at a specific number of degrees below its saturationtemperature. This allows the range of suitable temperatures for coolantstored in the reservoir 200 to be wider than if vaporization wererequired within the first heat sink module. This arrangement can allow alower cost and potentially more reliable control system to be used,which can be desirable in many applications.

In another example, a method of absorbing heat from two or moreprocessors 415 in an electronic device can involve flowing coolant 50through two or more fluidly connected heat sink modules 100 arranged ina series configuration. The method can include providing a flow 51 ofsubcooled single-phase liquid coolant 50 to a first heat sink module100-1, as shown in FIG. 98. The first heat sink module 100-1 can includea first thermally conductive base member 430 in thermal communicationwith a first processor in an electronic device. The subcooledsingle-phase liquid coolant 50 can have a predetermined pressure and apredetermined temperature at a first inlet 105 of the first heat sinkmodule 100-1. The predetermined temperature can be below a saturationtemperature of the subcooled single-phase liquid coolant at thepredetermined pressure. The method can include projecting the flow 51 ofsubcooled single-phase liquid coolant 50 against the thermallyconductive base member 430 within the first heat sink module 100-1. Theflow of subcooled single-phase liquid coolant can absorb a first amountof heat from the first processor 415 through the thermally conductivebase member 430 as sensible heat. Despite absorbing the first amount ofheat, the flow can remain subcooled single-phase liquid coolant 50 at atemperature below the coolant's saturation temperature. The method caninclude providing a second heat sink module 100-2 including a secondthermally conductive base member 430 in thermal communication with asecond processor 415. The second heat sink module 100-2 can include asecond inlet 105. The method can include providing a first section oftubing 225 having a first end connected to the first outlet 110 of thefirst heat sink module 100-1 and a second end connected to the secondinlet 105 of the second heat sink module 100-2, as shown in FIG. 98. Themethod can include transporting through the first section of tubing 225the flow of subcooled single-phase liquid coolant from the first outlet110 of the first heat sink module 100-1 to the second inlet 105 of thesecond heat sink module 100-2. The method can include projecting theflow 51 of subcooled single-phase liquid coolant 50 against the secondthermally conductive base member 430 within the second heat sink module100-2. The subcooled single-phase liquid coolant can absorb a secondamount of heat from the second processor 415 through the secondthermally conductive base member 430 as sensible heat resulting in thesubcooled single-phase liquid coolant reaching its saturationtemperature and becoming saturated single-phase liquid coolant. Thesaturated single-phase liquid coolant can absorb a third amount of heatfrom the second processor 415 through the second thermally conductivebase member 430 as latent heat resulting in vaporization of a firstportion of the saturated single-phase liquid coolant thereby changingthe flow 51 of saturated single-phase liquid coolant to two-phase bubblyflow comprising saturated liquid coolant with vapor coolant dispersed asbubbles 275 in the saturated liquid coolant 50.

The method can include directing the flow 51 of subcooled single-phaseliquid coolant through one or more series-connected heat sink modules100 prior to providing the flow of subcooled single-phase liquid coolantto the inlet 105 of the first heat sink module 100-1. The method caninclude transporting the flow 51 of two-phase bubbly flow containing thefirst amount of heat, the second amount of heat, and the third amount ofheat out of the electronic device through a flexible cooling line 225where it can be rejected to an external heat rejection loop 43.Providing a first section of tubing 225 can include providing a sectionof flexible tubing having a minimum bend radius of less than 3, 2.5, or2 inches to permit routing within the electronic device. Likewise,providing a flexible cooling line 303 can include providing a flexiblecooling line having a minimum bend radius of less than 3, 2.5, or 2inches to permit routing within the electronic device.

The electronic device can be a server 400, a personal computer, a tabletcomputer, a power electronics device, a smartphone, an automotiveelectronic control unit, a battery management device, a progressivegaming device, a telecommunications system, a high performance computingsystem, a server-based gaming device, an avionics system, or a homeautomation control unit. The first processor 415 can be a centralprocessing unit (CPU) or a graphics processing unit (GPU). Likewise, thesecond processor 415 can be a CPU or GPU.

In yet another example, a method of absorbing heat from two or moredevices can involve using a two-phase cooling apparatus configured topump low-pressure coolant 50 through two or more fluidly-connected andseries-connected heat sink modules 100. The method can include providinga flow 51 of subcooled single-phase liquid coolant 50 to an inlet 105 ofa first heat sink module 100-1 in thermal communication with a firstdevice. The flow 51 of subcooled single-phase liquid coolant 50 canabsorb a first amount of heat from the first device as sensible heatwithin the first heat sink module 100-1. The method can includetransporting the flow 51 of subcooled single-phase liquid coolant 50from an outlet 110 of the first heat sink module 100-1 to an inlet 110of a second heat sink module 100-2. The flow 51 of subcooledsingle-phase liquid coolant 50 absorbs a second amount of heat from thesecond device partially as sensible heat and partially as latent heatwithin the second heat sink module 100-2. As a result, the flow 51 ofsubcooled single-phase liquid coolant can become two-phase bubbly flowhaving saturated liquid coolant with vapor bubbles 275 of coolantdispersed in the saturated liquid coolant. The method can includetransporting the two-phase bubbly flow including the first amount ofheat and the second amount of heat away from the first and seconddevices. The first and second amounts of heat can be rejected to anexternal heat rejection loop 43 by directing the two-phase bubbly flowthrough a heat exchanger 40 in thermal communication with the externalheat rejection loop 43.

Parallel-Connected Heat Sink Modules

FIG. 16 shows a schematic of a cooling apparatus 1 having a primarycooling loop 300 that includes three parallel cooling lines where eachparallel cooling line includes three heat sink modules 100 fluidlyconnected in series. The cooling apparatus shown in FIG. 16 can beconfigured to cool nine independent heat-generating surfaces 12, such asnine microprocessors 415. Other variations of the cooling apparatus 1shown in FIG. 16 can include more than three parallel cooling lines, andeach cooling line can include more than three series-connected modules100.

As shown in the schematic of FIG. 16, additional heat sink modules 100can be added to the cooling apparatus 1 in parallel cooling loops 300that they are serviced by, for example, the same pump 20, reservoir 200,and heat exchanger 40. Alternatively, as shown in FIG. 17, the coolingapparatus 1 can include additional reservoirs 200, pumps 20, and/or heatexchangers 40 in parallel for the purpose of redundancy and reliability.As used herein, an additional component “in parallel” refers to acomponent in fluid communication with the other components in a mannerthat bypasses only components of the same type without bypassingdifferent types of components. An example of an additional componentadded in parallel is shown with the additional heat sink modules 100 inFIG. 16, where three parallel cooling loops 300 are provided that eachare serviced by the same reservoir 200 and pump 20.

Mounting Bracket for Heat Sink Module

In some examples, it can be desirable to secure the heat sink module 100to a device using a mounting bracket 500. For instance, it can bedesirable to secure the sink module 100 tightly to a heat-providingsurface 12 to reduce thermal resistance and improve heat transfer rates.More specifically, when installing a heat sink module 100 on amicroprocessor 415, it can be desirable to use a mounting bracket 500 tosecure the heat sink module 100 firmly in place, as shown in FIGS.84-89. FIG. 84 shows a top perspective view of two series-connected heatsink modules 100 installed on top of microprocessors 415 in a server400. The mounting bracket 500 can attach to existing mounting holes 406in the motherboard 405 originally intended for an air-cooled heat sink,as shown in FIG. 84. Threaded fasteners 115 can secure the mountingbracket 500 to the threaded holes 406 in the motherboard 405. When thethreaded fasteners 115 are secured in the mounting holes 406, themounting bracket 500 can contact and apply a clamping force to a topsurface 160 of the heat sink module 100, thereby preventing the heatsink module 100 from shifting out of place during use.

The mounting brackets 500 shown in FIG. 84 are suitable forinstallations where the heat sink modules 100 can be aligned with themicroprocessor 415 and where there is ample room to route flexiblecooling lines 303 that transport coolant (i.e. working fluid) 50 to andfrom the heat sink modules. However, in many instances, routing theflexible cooling lines 303 can be difficult due to space constraints. Insome installations, greater mounting flexibility may be required. FIG.85 shows a top view of an S-shaped mounting bracket 500 that can connectto two holes in a motherboard 405 and can permit the heat sink module100 to be mounted in any suitable orientation, independent of theorientation of the microprocessor 415. By reducing mounting constraintsand the number of fasteners required, the S-shaped mounting bracket 500can allow for much shorter installation times and can alleviate stresson flexible cooling lines 303 and the potential for kinking by reducingthe need for tight bend radiuses that may be otherwise be required.Having greater options for orienting the heat sink module 100 can alsoallow significantly less flexible tubing 225 to be used in aninstallation, since routing options can be more direct than theconfiguration shown in FIG. 84 where the heat sink module 100 is alignedwith the microprocessor 415.

The S-shaped bracket 500 can include an S-shaped bracket member having afirst end and a second end, as shown in FIGS. 86-91. The S-shapedbracket member can include a first curvilinear portion 510 locatedbetween the first end and a midpoint. The S-shaped bracket can include asecond curvilinear portion 510 located between the midpoint and thesecond end. The first curvilinear portion can have a radius of curvatureof about 1.0-4.0, 1.0-2.5, or 1.5-2.0 inches. Similarly, the secondcurvilinear portion can have a radius of curvature of about 1.0-4.0,1.0-2.5, or 1.5-2.0 inches.

The bracket 500 can include a first slot 505 proximate the first end anda second slot 505 proximate a second end. The first and second slots 505can be elongated openings that allow for imperfect alignment with themounting holes in the motherboard 405. In some examples, the fasteners115 that mount the S-shaped bracket 500 to the mounting holes in themotherboard 405 can each include a washer to distribute a clamping loadacross a larger surface area of the bracket near the first and secondslots 505.

In some examples, the first slot 505 can be substantially parallel tothe second slot 505. The first slot 505 can have a first midpointlocated a first distance from the midpoint of the bracket 500.Similarly, the second slot can have a second midpoint located a seconddistance from the midpoint of the bracket 500. The first distance andthe second distance can be about equal, thereby providing a bracket thatis symmetrical so that an installer does not have to be concerned withproperly orienting the bracket during assembly.

The S-shaped bracket can provide a larger contact area against the topsurface 160 of the heat sink module 100 than a linear mounting bracket,thereby allowing the clamping force to be distributed over a greaterpercentage of the top surface 160 of the heat sink module 100 andthereby mitigating risks of cracking or crushing the polymer heat sinkmodule 100 during installation if the fasteners are over-tightened.

Single Heat Sink Module for Multiple Heat Sources

To reduce installation costs, it can be desirable to cool more than oneheat source 12 using a single heat sink module 100. Exampleinstallations are shown in FIGS. 66 and 67. FIG. 66 shows an example ofan existing server 400 with a heat sink module retrofitted thereon. Theserver 400 includes a motherboard 405, two microprocessors 415 mountedon the motherboard, and a finned heat sink 440 mounted on eachmicroprocessor 415. Rather than spend time and effort removing thefinned heat sink modules 440 already installed on the microprocessors415, instead, a thermally conductive base member 430 can be placed inthermal contact with both finned heat sinks 440, as shown in FIG. 66.The thermally conductive base member 430 can extend from a first finnedheat sink 440 to a second finned heat sink 440. A heat sink module 100can be mounted on a surface 12 of the thermally conductive base member430. By directing a plurality of jet streams 16 of coolant at thesurface to be cooled 12 of the thermally conductive base member 430, theconfiguration shown in FIG. 66 can cool two microprocessorssimultaneously at a lower cost than installing two heat sink modules andwithout having to uninstall any factory-installed components of theserver (e.g. the finned heat sinks 440). By not uninstallingfactory-installed hardware, this cooling method can avoid potentiallyvoiding a factory warranty on the server 400 or computer.

FIG. 67 shows an arrangement where a thermally conductive base member430 extends from a first microprocessor 415 to a second microprocessor415 mounted on a motherboard 405. A heat sink module 100 can be mountedon a surface 12 of the thermally conductive base member 430. Bydirecting a plurality of jet streams 16 of coolant at the surface to becooled 12 of the thermally conductive base member 430, the configurationshown in FIG. 67 can cool two microprocessors 415 simultaneously at alower cost than using two heat sink modules. To ensure even cooling ofeach microprocessor, it can be desirable for the thermally conductivebase member 430 to make contact with an entire, or substantially theentire, top surface of each microprocessor, as shown in FIG. 67.

Surface to be Cooled

The surface to be cooled 12 can be exposed within the outlet chamber 150of the heat sink module 100, such that the jet streams 16 of coolant 50impinge directly on the surface to be cooled 12 without thermalinterference materials disposed between the surface 12 and the coolant50. As used herein, “surface to be cooled” refers to any electronic orother device having a surface that generates heat and requires cooling.Non-limiting, exemplary surfaces to be cooled 12 include microprocessors415, microelectronic circuit chips in supercomputers, power electronics,mechanical components, process containers, or any electronic circuits ordevices requiring cooling, such as diode laser packages. The surface tobe cooled 12 can be exposed within the outlet chamber 150 of the heatsink module 100 by constructing the outlet chamber to include thesurface 12 within the chamber 150 or by constructing the outlet chambersuch that the surface to be cooled 12 serves as a bounding wall of theoutlet chamber 150, as shown in FIG. 26. In some examples, the heat sinkmodule 100 can form an enclosure, such as a sealed liquid-tightenclosure, against the surface to be cooled 12 using one or more sealingmembers (e.g. o-rings, gaskets, or adhesives).

In some examples of the cooling apparatus 1, coolant 50 can be deliveredto a heat sink module 100 that is mounted directly on a surface to becooled, such as a surface of a microprocessor 415 that is electricallyconnected to a motherboard 405, as shown in FIG. 27. In other examples,the heat sink module 100 can be mounted on a thermally conductiveintermediary object, such as a thermally conductive base member 430, asshown in FIG. 26. The assembly of the heat sink module 100 and thethermally conductive base member 430 can then be mounted on a heatsource, such as a microprocessor 415 electrically connected to amotherboard 405, as show in FIG. 28. A layer of thermal interfacematerial (e.g. solder thermal interface material or polymer thermalinterface material) can be applied between a top surface of the heatsource (e.g. microprocessor) and a bottom surface of the thermallyconductive base member 430. The thermally conductive base member 430 canbe made of a material with a high thermal conductivity, such as copper,silver, gold, aluminum, or tungsten.

The thermally conductive member 430 can be placed in thermalcommunication with an electronic device, or other type of device, thathas a surface 12 that generates heat and requires cooling, such as amicroprocessor 415, microelectronic circuit chip in a supercomputer, orany other electronic circuit or device requiring cooling, such as diodelaser packages.

Three-Phase Contact Line Length

FIG. 63 shows a top view of a heated surface 12 covered by coolant 50,where the coolant has regions of vapor coolant 56 and wetted regions ofliquid coolant 57 in contact with the heated surface 12. The dark areasin FIG. 63 show the vapor coolant regions 56, and the light areas showthe liquid coolant regions 57. A length of a three-phase contact line 58is measured as a sum of all curves where liquid coolant 57, vaporcoolant 56, and the solid heated surface 12 are in mutual contact on theheated surface 12. The three-phase contact line 58 length can bedetermined using suitable image processing techniques.

The heat transfer rate from the surface to be cooled 12 to the coolant50 has been shown to strongly correlate with the length of thethree-phase contact line 58 on the surface to be cooled 12.Consequently, increasing the length of the three-phase contact line 58can be desirable when attempting to increase the heat transfer rate fromthe surface to be cooled. Increasing the heat transfer rate isdesirable, since it increases the efficiency of the cooling apparatus 1and allows higher heat flux surfaces to be cooled by the coolingapparatus.

By providing jet streams 16 of coolant that impinge the surface to becooled 12 from a suitable jet height 18, the heat sink modules 100described herein effectively increase the length of the three-phasecontact line 58. Consequently, the heat sink modules 100 describedherein provide much higher heat transfer rates than competing coolingsystems. By selecting orifice 155 diameters, jet heights 18, coolantpressures, and orifice orientations from the ranges provided herein, theheat sink module 100 can provide jet streams 16 with sufficient momentumto disrupt vapor formation on the surface to be cooled 12, therebyincreasing the length of the three-phase contact line 58 on the surfaceto be cooled 12 and thereby allowing higher heat fluxes to beeffectively dissipated without reaching critical heat flux.

Redundant Cooling Apparatus

In some examples, it can be desirable to have a fully redundant coolingapparatus 2 where each heat-generating surface 12 is cooled by at leasttwo completely independent cooling apparatuses 1. In the event offailure of a first independent cooling apparatus 1, a second independentcooling apparatus 1 can be configured to provide sufficient coolingcapacity to adequately cool the heat-generating surface 12 and therebyavoid any downtime or reduction in performance when the heat-generatingsurface 12 is, for example, a microprocessor 415 or other criticalsystem component. In a fully redundant cooling apparatus 2, theheat-generating component 12 can be adequately cooled by a first coolingapparatus 1 (and can continue to operate normally) while repairs aremade on a failed component within a second cooling apparatus 1 of theredundant cooling apparatus 2.

FIG. 9 shows a front perspective view of a fully redundant coolingapparatus 2 installed on eight racks 410 of servers 400 in a data center425. The redundant cooling apparatus 2 includes a first independentcooling apparatus 1 and a second independent cooling apparatus, eachsimilar to the cooling apparatus 1 described with respect to FIGS. 1-3.FIG. 10 shows a rear view of the redundant cooling apparatus 2 of FIG.9. In FIGS. 9 and 10, the redundant cooling apparatus 2 has a first pump20, a first reservoir 200, a first set of inlet and outlet manifolds,and a first heat exchanger 40 associated with the first independentcooling apparatus 1. Likewise, the redundant cooling apparatus 2 has asecond pump, a second reservoir, a second set of inlet and outletmanifolds, and a second heat exchanger 40 associated with the secondindependent cooling apparatus 1.

In some examples, the first and second cooling apparatuses 1 may not befully independent and may share components that have a very lowlikelihood of failure, such as a common reservoir 200 and/or a commonheat exchanger 40. FIGS. 69 and 70 shows schematics of redundant coolingapparatuses 2 that have a common reservoir 200. Such an arrangement maybe useful where a redundant cooling apparatus 2 is desired but wheresafety regulations restrict the volume of coolant that can be used in aconfined space. The configuration shown in FIGS. 69 and 70 may alsoreduce system cost by reducing the total number of components and byreducing the volume of coolant used.

FIG. 17 shows a schematic of a redundant cooling apparatus 2 having aredundant heat sink module 700 mounted on a heat source 12. Theredundant heat sink module 700 is connected to two a first independentcooling apparatus 1 and a second independent cooling apparatus 1. Thefirst independent cooling apparatus includes a primary cooling loop 300,a first bypass, and a second bypass 310. Similarly, the secondindependent cooling apparatus includes a primary cooling loop 300, afirst bypass 305, and second bypass 310. As a result of thisconfiguration, failure of a single component in the first independentcooling apparatus 1 will not disrupt operation of the second independentcooling apparatus 1. The redundant cooling apparatus 2 is configured toprovide adequate cooling of the surface to be cooled 12 even if thefirst or second independent cooling apparatus 1 fails.

Although the redundant cooling apparatus 2 shown in FIG. 17 incorporatestwo cooling apparatuses 1 like the one presented in FIG. 11A, this isnot limiting. Any of the non-redundant cooling apparatuses 1 presentedin FIGS. 11A, 12A-12T, 13, 14A, and 16 can be used, in any combination,to provide a redundant cooling apparatus 2 to cool one or more heatgenerating surfaces 12.

In any of the schematics described herein or shown in the accompanyingfigures, each redundant heat sink module 700 can be a combination of twoheat sink modules 100 of the type shown in FIG. 21, or a redundant heatsink module 700 with integrated independent coolant pathways, as shownin FIGS. 51A-51M. Therefore, the redundant heat sink module(s) 700 inFIGS. 17 and 18 can be exchanged for two heat sink modules 100 of thetype shown in FIG. 21. In some examples, two non-redundant heat sinkmodules 100 can be mounted to a thermally conductive base member 430 toprovide a redundant heat sink assembly, as shown in FIG. 52B.

FIG. 18 shows a schematic of a redundant cooling apparatus 2 that ismore complex than the schematic shown in FIG. 17. The redundant coolingapparatus 2 in FIG. 18 includes a first independent cooling apparatus 1and a second independent cooling apparatus 1. Each independent coolingapparatus 1 includes two parallel cooling lines where each parallelcooling line is fluidly connected to three redundant heat sink modules700 arranged in a series configuration. As a result, the redundantcooling apparatus 2 shown in FIG. 17 is capable of redundantly coolingsix surfaces to be cooled 12. The redundant cooling apparatus 2 isscalable, and additional parallel and series connected heat sink modules700 can be added to cool additional surfaces 12.

FIG. 19 shows a top view of a redundant cooling apparatus 2 installed ina data center or computer room 425 having twenty racks 410 of servers400. Each independent cooling apparatus 1 of the redundant coolingapparatus 2 can be fluidly connected to a heat exchanger 40 locatedinside of the room 425 where the servers are located. In some examples,the heat exchanger 40 can reject heat into the room 425, and a CRAC canbe used to remove the rejected heat from the room.

FIG. 20 shows a top view of a redundant cooling apparatus 2 installed ina data center or computer room 425 having twenty racks 410 of servers400. Each independent cooling apparatus 1 of the redundant coolingapparatus 2 can be fluidly connected to any suitable external heatexchanger 40 located outside of the room 425 where the servers arelocated. Each independent cooling apparatus 1 can be fluidly connectedto the external heat exchanger 40 by an external heat rejection loop 43that circulates an external cooling fluid, such as water or awater-glycol mixture. In some examples the heat exchanger 40 can beconnected to a chilled water system of a building where the room 425 islocated. In other examples, the heat exchanger 40 can be anair-to-liquid dry cooler or a liquid-to-liquid heat exchanger locatedoutside of the room 425 (e.g. located outside of the building).

As noted above, FIGS. 69 and 70 shows schematics of redundant coolingapparatuses 2 having a first and second cooling apparatus where thefirst and second cooling apparatuses are not fully independent, sincethey share a common reservoir. In FIG. 69, the first and second coolingapparatuses 1 also share a common heat rejection loop 43. The heatrejection loop 43 is fluidly connected to the common reservoir 200 andincludes a pump 20 and a heat exchanger 40. The pump 20 is configured tocirculate a flow 51 of coolant from the reservoir 200 through the heatexchanger 40, where heat is removed from the flow of coolant, therebyreducing the temperature of the flow of coolant. The heat exchanger canbe located outside of a room 425 where the redundant cooling apparatus 2is installed so that heat rejected from the flow of coolant is notdischarged back into the room 425. For instance, the heat exchanger 40can be located on a rooftop of a building where the redundant coolingapparatus 2 is installed.

In FIG. 70, the first and second cooling apparatuses 1 share a commonreservoir 200, but have separate heat rejection loops 43, also known assecond bypasses 310. Each heat rejection loop 43 includes a pressureregulator 60 and a heat exchanger 40. In some examples, each pressureregulator 60 can be adjusted (manually or automatically) to allow about30-60 or 45-55% of the flow 51 leaving each pump 20 to circulate througheach heat rejection loop 43. This configuration can ensure that thecoolant stored in the reservoir 200 remains sufficiently sub-cooled toallow for rapid condensing of any vapor delivered to the reservoir forma first or second return line 230 carrying bubbly flow. By rapidlycondensing vapor within the reservoir 200 through direct interactionwith a relatively large volume of sub-cooled liquid, the redundantcooling apparatus 2 prevents vapor from being delivered from thereservoir 200 outlets to either pump.

Redundant Heat Sink Module

FIG. 51A shows a top perspective view of a redundant heat sink module700. The heat sink module 700 can be defined by a front side surface175, a rear side surface 180, a left side surface 185, a right sidesurface 190, a top surface 160, and a bottom surface 135. FIG. 51B showsa top view of the redundant heat sink module of FIG. 51A, where a firstindependent coolant pathway 701 and the second independent coolantpathway 702 are represented by dashed lines. In the example shown inFIG. 51B, the first independent coolant pathway 701 passes through afirst region near a middle of the redundant heat sink module 700, andthe second independent coolant pathway 702 passes through a secondregion outside of the perimeter of the first region. The first andsecond independent coolant pathways (701, 702) can be completelyindependent, meaning that no amount (or no substantial amount) ofcoolant 51 is transferred from the first independent coolant pathway 701to the second independent coolant pathway 702 or vice versa. The firstindependent coolant pathway can extend from a first inlet port 105-1 toa first outlet port 110-1 of the redundant heat sink module 700.Similarly, a second independent coolant pathway 702 can extend from asecond inlet port 105-2 to a second outlet port 110-2 of the redundantheat sink module 700.

The first independent coolant pathway 701 can include a first inletpassage 165-1 extending from the first inlet port 105-1 to a first inletchamber 145-1, as shown in FIG. 51F, which shows a cross-sectional viewof FIG. 51 E taken along section A-A. The first inlet chamber 145-1 canhave a tapered geometry to provide an even distribution of coolant tothe plurality of orifices 155-1. For a redundant heat sink module 700configured to cool a microprocessor 415, the first inlet chamber 145-1can taper from a maximum height of about 0.040-0.120 in. to a minimumheight of about 0.020-0.040 in. The first inlet chamber 145-1 can have awidth of about 0.75-1.5 in. and a length of about 0.75-1.5 in. Thevolume of the first inlet chamber 145-1 can be about 0.01-0.02,0.01-0.05, 0.04-0.08, 0.07-0.15, 0.1-0.2, 0.15-0.25, 0.2-0.4, 0.3-0.5in³, or preferably about 0.15 in³. The first outlet chamber 150-1 can beslightly larger than the first inlet chamber 145-1 to accommodateexpansion of a portion of the coolant 50 as it changes phase from liquidto vapor. For example, the first outlet chamber 15 can have a volume ofabout 0.02-0.05, 0.04-0.08, 0.07-0.15, 0.1-0.2, 0.15-0.25, 0.2-0.4,0.3-0.5, 0.4-0.75 in³, or preferably about 0.25 in³. Although the firstinlet and outlet chambers (145-1, 150-1) can be made larger, thedimensions provided above provide a high-performing, compact heat sinkmodule 700.

As shown in the top view of the FIG. 51E, the second independent coolantpathway 702 is bifurcated and circumscribes the first independentcoolant pathway 701. Consequently, the second inlet chamber 145-2 andthe second outlet chamber 150-2 are also bifurcated, as shown in FIG.51I. Despite having a different geometry than the first inlet chamber145-1, the bifurcated second inlet chamber 145-2 can have about the sametotal volume as the first inlet chamber 145-1. For example, the volumeof the first inlet chamber 145-1 can be about 0.01-0.02, 0.01-0.05,0.04-0.08, 0.07-0.15, 0.1-0.2, 0.15-0.25, 0.2-0.4, 0.3-0.5 in³, orpreferably about 0.15 in³. Likewise, despite having a different geometrythan the first outlet chamber 150-1, the bifurcated second outletchamber 150-2 can have about the same total volume as the first outletchamber 150-1. For example, the volume of the second outlet chamber150-2 can be about 0.02-0.05, 0.04-0.08, 0.07-0.15, 0.1-0.2, 0.15-0.25,0.2-0.4, 0.3-0.5, 0.4-0.75 in³, or preferably about 0.25 in³.

As shown in FIG. 51F, a first plurality of orifices 155-1 can extendfrom the first inlet chamber 145-1 to a first outlet chamber 150-1 andcan be configured to provide a plurality of jet streams 16 of coolantinto the first outlet chamber 150-1 when pressurized coolant is providedto the first inlet chamber 145-1. A first outlet passage 166-1 canextend from the first outlet chamber 150-1 to the first outlet port110-1, as shown in FIG. 51G, which is a cross-sectional view of FIG. 51Etaken along section B-B.

A first plurality of anti-pooling orifices 156-1 can extend from thefirst inlet chamber 145-1 to a location proximate a rear wall of thefirst outlet chamber 150-1 and can be configured to provide a pluralityof jet streams 16 of coolant proximate a rear wall of the first outletchamber 150-1 when pressurized coolant is provided to the first inletchamber 145-1. The anti-pooling jet streams 16 can be configured toimpinge the surface to be cooled 12 at an angle near the rear wall andto prevent pooling of coolant near a rear wall of the first outletchamber 150-1 by promoting directional flow away from the rear wall. Bypreventing pooling, the anti-pooling jet streams can prevent the onsetof critical heat flux near the rear wall of the first outlet chamber150-1, thereby increasing a maximum thermal load the heat sink module iscapable of safely dissipating.

The second independent coolant pathway 702 can include a second inletpassage 165-2 extending from the second inlet port 105-2 to a secondinlet chamber 145-2, as shown in FIG. 51G. A second plurality oforifices 155-2 can extend from the second inlet chamber 145-2 to asecond outlet chamber 150-2 and can be configured to provide a pluralityof jet streams 16 of coolant into the second outlet chamber 150-2 whenpressurized coolant is provided to the second inlet chamber 145-2. Asecond outlet passage 166-2 can extend from the second outlet chamber150-2 to the second outlet port 110-2, as shown in FIG. 51 F. A secondplurality of anti-pooling orifices 156-2 can extend from the secondinlet chamber 145-2 to a location proximate a rear wall of the secondoutlet chamber 150-2 and can be configured to provide a plurality of jetstreams 16 of coolant proximate the rear wall of the second outletchamber 150-2 when pressurized coolant is provided to the second inletchamber 145-2.

FIG. 51D shows a bottom view of the redundant heat sink module 700 ofFIG. 51A. The first independent coolant pathway 701 includes an array oforifices 155 arranged in a first region located near a middle portion ofthe module 700. The second independent coolant pathway 702 includes anarray of orifices 155 arranged in a second region located beyond (e.g.outside of or circumscribing) the perimeter of the first region. Inother examples, the first region can be located near a first half of themodule 700 and the second region can be located near a second half ofthe module 700, as shown in the side-by-side coolant pathway example ofFIG. 53.

The first outlet chamber 150-1 of the redundant heat sink module 700 canhave an open portion that can be enclosed by a surface to be cooled 12when the redundant heat sink module 700 is installed on the surface tobe cooled 12. Similarly, the second outlet chamber 150-2 of theredundant heat sink module 700 can have an open portion that can beenclosed by a surface to be cooled 12 when the redundant heat sinkmodule 700 is installed on the surface to be cooled 12.

To facilitate sealing against the surface to be cooled 12, the redundantheat sink module 700 can include a first sealing member 125-1 and asecond sealing member 125-2, as shown in FIG. 51D. The first sealingmember 125-1 (e.g. o-ring, gasket, sealant) can be disposed within afirst channel 140-1 formed in a bottom surface 135 of the redundant heatsink module 700. The first channel 140-1 can circumscribe the firstoutlet chamber 150-1, and the first sealing member 125-1 can becompressed between the first channel 140-1 and the surface to be cooled12 to provide a liquid-tight seal therebetween. The redundant heat sinkmodule 700 can include a second sealing member 125-2, as shown in FIG.51D. The second sealing member 125-2 (e.g. o-ring, gasket, sealant) canbe disposed within a second channel 140-2 formed in the bottom surface135 of the redundant heat sink module 700. The second channel 140-2 cancircumscribe the second outlet chamber 150-2, and the second sealingmember 125-2 can be compressed between the second channel 140-2 and thesurface to be cooled 12 to provide a liquid-tight seal therebetween. Inthis example the first sealing member 125-1 can provide a liquid-tightseal between the first outlet chamber 150-1 and the second outletchamber 150-2. The first sealing member 125-1 can bound an innerperimeter of the second outlet chamber 150-2, and the second sealingmember 125-2 can bound an outer perimeter of the second outlet chamber150-2.

FIG. 51I shows a cross-sectional view of the redundant heat sink module700 taken along section C-C shown in FIG. 51H. FIG. 51I shows relativepositioning of a first inlet chamber 145-1, a first outlet chamber150-1, a bifurcated second inlet chamber 145-2, and a bifurcated secondoutlet chamber 150-2. A first dividing member 195-1 separates the firstinlet chamber 145-1 from the first outlet chamber 150-1. The firstplurality of orifices 155-1 extend from the first inlet chamber 145-1 tothe first outlet chamber 150-1 and through the first dividing member195-1. Similarly, the second inlet chamber 145-2 is separated from thesecond outlet chamber 150-2 by a second dividing member 195-2. Thesecond plurality of orifices 155-2 extend from the second inlet chamber145-2 to the second outlet chamber 150-2 and through the second dividingmember 195-2. The thickness of the first and second dividing members(195-1, 195-2) can be selected to ensure that the orifices havesufficient L/D ratios and that the heat sink module 700 is structurallysound (i.e. capable of handling a flow 51 of pressurized coolant).

FIG. 51K shows a side cross-sectional view of the redundant heat sinkmodule 700 of FIG. 51J taken along section D-D. The nonlinear sectionalview exposes a substantial portion of the first independent coolantpathway 701, including the first inlet port 105-1, first inlet passage165-1, first inlet chamber 145-1, the first plurality of orifices 155-1,the first anti-pooling orifice 156-1, the first outlet chamber 150-1,the first outlet passage 166-1, and the first outlet port 110-1. Theapparent blockages between the first inlet passage 165-1 and the firstinlet chamber 145-1 and between the first outlet chamber 150-1 and thefirst outlet passage 166-1 are simply artifacts of the location ofsection D-D. No such blockages exist in the first coolant pathway 701.The first coolant pathway 701 is designed to be free flowing such thatonly a small pressure drop (e.g. about 1.5 psi) is observed between thefirst inlet port 105-1 and the first outlet port 110-1 when pressurizedcoolant is delivered to the first coolant pathway 701.

As shown in FIG. 51K, the first inlet chamber 145-1 can have a taperedgeometry that ensures substantially similar flow through each orifice155. The first outlet chamber 150-1 can have an expanding geometry thatallows for expansion of the coolant as a portion of the coolant changesphase from a liquid to a vapor as heat is transferred from the surfaceto be cooled 12 to the flow of coolant 50. The redundant heat sinkmodule 700 can include a flow-guiding lip 162, as shown in FIG. 51K. Theflow-guiding lip 162 can guide the directional flow 51 from the outletchamber 150-1 to the outlet passage 166-1. Preferably, the flow-guidinglip can have an angle of less than about 45 degrees with respect to thesurface to be cooled 12 to avoid creating a flow restriction orstagnation region proximate the exit of the outlet chamber 150-1.

FIG. 51M shows a side cross-section view of the redundant heat sinkmodule 700 of FIG. 51L taken along section E-E. The nonlinear sectionalview exposes a substantial portion of the second independent coolantpathway 702, including the second inlet port 105-2, second inlet passage165-2, second inlet chamber 145-2, the second plurality of orifices155-2, the second anti-pooling orifice 156-2, the second outlet chamber150-2, the second outlet passage 166-2, and the second outlet port110-2.

The apparent discontinuity between the second outlet chamber 150-2 onthe left and the second outlet chamber 150-2 on the right is simply anartifact of the location of section E-E. No such discontinuity exists inthe second coolant pathway 702. The second coolant pathway 702 isdesigned to be free flowing such that only a small pressure drop (e.g.about 1.5 psi) is observed between the second inlet port 105-2 and thesecond outlet port 110-2 when pressurized coolant is delivered to thesecond coolant pathway 702.

FIG. 51 N shows flow vectors associated with the first coolant pathway701 and flow vectors associated with the second coolant pathway 702. Toprovide an even flow distribution across the inlets of the plurality oforifices 155-1 in the first inlet chamber 145-1, the first coolantpathway 701 can include a flow diverter 706, as shown in FIG. 51N. Theflow diverter 706 can have a shape similar to an airfoil with a curvedsurface 706. As a result of fluid dynamics, the curved surface 706causes incoming coolant to flow in close proximity to the curvature ofthe curved surface 706, similar to the way air flow follows thecurvature of a wing. Without the flow diverter 706, the incoming flowwould hug a left perimeter of the first coolant pathway 701 andpotentially starve orifices 155 located near a center or right perimeterof the array of orifices.

FIG. 51O is a top view of the redundant heat sink module 700. The firstcoolant pathway 701 has a first inlet port 105-1 and a first outlet port110-1, and the second coolant pathway 702 has a second inlet port 105-2and a second outlet port 110-2. In some examples, coolant can enter thefirst inlet port 105-1 as liquid flow and exit the first outlet port110-1 as two-phase bubbly flow. Likewise, coolant can enter the secondinlet port 105-2 as liquid flow and exit the second outlet port 110-2 astwo-phase bubbly flow.

When cooling a heated surface 12 that experiences rapid increases inheat flux, such as an electric motor of an electric vehicle, it can bedesirable to configure the redundant cooling apparatus 2 to managetransient heat loads without experiencing critical heat flux. In oneexample, the redundant heat sink module 700 can be operated as shown inFIG. 51Q. In this example, during normal operation, when the heatedsurface is producing a moderate heat flux, a first coolant pathway 701can be operated so that two-phase bubbly flow is formed therein, and asecond coolant pathway 702 can be operated so that little or no vapor isformed therein. If the heat load increases rapidly, it will cause phasechange within the second coolant pathway 702, which will provideadditional cooling capacity for the increased heat load. Achievingparallel flows of bubbly flow and liquid flow can be achieved in severalpossible ways. Where both coolant pathways are transporting the sametype of coolant (e.g. HFE-7000), the flow rate of coolant 50 in thesecond cooling pathway 702 can be increased until no vapor formstherein. Due to its higher flow rate, the second cooling pathway 702will have greater cooling capacity than the first coolant pathway 701,and will be able to safely manage rapid increases in heat flux andthereby avoid onset of critical heat flux. In this example, the pressureof the flow 51 of coolant in the second coolant pathway 702 can be sethigher than the pressure of the flow of coolant in the first coolantpathway 701 to provide a higher saturation temperature in the secondcoolant pathway 702 than in the first coolant pathway 701. In anotherexample, the first coolant pathway 701 can transport a first coolanthaving a first boiling point, and the second coolant pathway 702 cantransport a second coolant having a second boiling point, where thesecond boiling point is higher than the first boiling point. In onespecific example, the first coolant can be HFE-7000 with a boiling pointof 34 degrees C. at one atmosphere, and the second coolant can beHFE-7100 with a boiling point of 61 degrees C. at one atmosphere. Theflow rate and/or pressure of the second coolant can be increased toprovide excess cooling capacity in the second coolant pathway to safelymanage rapid increases in heat flux and thereby avoid onset of criticalheat flux.

FIG. 51P shows a top view of the redundant heat sink module similar toFIG. 51Q, except that the first coolant pathway 701 is transporting aflow of liquid coolant, and the second coolant pathway 702 istransporting two-phase bubbly flow. For heat sources that havenon-uniform heat distributions, such as multi-core processors, it can bedesirable to select a configuration where the coolant pathway withexcess cooling capacity (i.e. the coolant pathway that is transporting aflow of liquid coolant) is situated over the portion of the heat sourcethat is likely to experience a rapid increase in heat flux.

Dimensions, volumes, and/or ratios associated with orifices (155, 156),chambers (145, 150), ports (105, 110), passages (165, 166), jet heights18, boiling inducing members 196, and dividing members 195 describedherein with respect to the non-redundant heat sink modules 100 alsoapply to corresponding features of the redundant heat sink modules 700.Coolant pressures and flow rates described herein with respect tonon-redundant heat sink modules 100 also apply to each independentcoolant pathway (701, 702) in the redundant heat sink modules 700.

Portable Servicing Unit

A portable servicing unit can be provided to aid in draining the coolingapparatus 1, for example, when servicing or repairing the coolingapparatus. The portable servicing unit can include a vacuum pump. Theportable servicing unit can include a hose, such as a flexible hose,having a first end a second end. A first end of the hose can beconfigured to fluidly connect to an inlet of the vacuum pump of theportable servicing unit. A second end of the hose can be configured tofluidly connect to a connection point (e.g. a drain 245) of the coolingapparatus 1 through, for example, a threaded fitting or a quick-connectfitting. The portable machine can include a portable reservoir fluidlyconnected to an outlet of the vacuum pump. When connected to the coolingapparatus 1 and activated, the vacuum pump of the portable servicingunit can apply vacuum pressure to the cooling apparatus 1 by way of thehose, which results in coolant flowing from the cooling apparatus,through the hose and vacuum pump, and into the portable reservoir. Whenservicing is complete, fluid from the portable reservoir can be pumpedback into the cooling system or transported to an appropriate disposalor recycling facility. In some examples, the portable servicing unit caninclude one or more thermoelectric heaters. The thermoelectric heaterscan be placed in thermal communication with components of the coolingapparatus 1, and by transferring heat to coolant within the apparatus,the thermoelectric heaters can promote evacuation of fluid from theapparatus through a drain 245 or other access point in the apparatus.

3D Printing

One or more components of the cooling apparatus 1 can be manufactured bya three-dimensional printing process. The heat sink module 100,redundant heat sink module 700, or portions of either heat sink module,such as an insertable orifice plate 198 or module body 104, can bemanufactured by a three-dimensional printing process. One example of asuitable 3D printer is a Form 1+SLA 3D Printer from Formlabs Inc. ofSomerville, Mass. One example of a suitable material for SLA 3D printingis Accura Bluestone Plastic from 3D Systems.

In some examples, a three-dimensional manufacturing process can be usedto create tubing 225 used to fluidly connect a first heat sink module100 to a second heat sink module, such as the section of tubing shown inFIG. 73. In some examples, a three-dimensional printing process can beused to form a combined heat sink module 100 and section of tubing 225to eliminate connectors 120 and potential leak points. In some examples,a three-dimensional printing process can be used to form two heat sinkmodules 100 fluidly connected by a section of tubing 225, similar to theconfiguration shown in FIG. 73. This approach can eliminate potentialleak points that would typically exist, for example, at threadedconnections where fittings attach a section of tubing 225 to an inlet oroutlet port (105, 110) of the heat sink modules. This approach can alsoreduce installation time and avoid installation errors.

In some examples, components of the cooling apparatus 1 can be formed bya stereolithography process that involves forming layers of materialcurable in response to synergistic stimulation adjacent to previouslyformed layers of material and successively curing the layers of materialby exposing the layers of material to a pattern of synergisticstimulation corresponding to successive cross-sections of the heat sinkmodule. The material curable in response to synergistic stimulation canbe a liquid photopolymer.

Coolant Temperature, Pressure, and Flow Rate

In some examples, it can be desirable to maintain coolant surrounding asurface to be cooled 12 at a pressure that results in the saturationtemperature of the coolant being slightly above the temperature of jetstreams of coolant being projected at the surface to be cooled 12. Asused herein, “maintain” can mean holding at a relatively constant valueover a period of time. “Coolant surrounding a surface” refers to asteady state volume of coolant immediately surrounding and in contactwith the surface to be cooled 12, excluding jet streams 16 of coolantprojected directly at the surface to be cooled 12. “Saturationtemperature” is used herein as is it is commonly used in the art. Thesaturation temperature is the temperature for a given pressure at whicha liquid is in equilibrium with its vapor phase. If the pressure in asystem remains constant (i.e. isobaric), a liquid at saturationtemperature evaporates into its vapor phase as additional thermal energy(i.e. heat) is applied. Similarly, if the pressure in a system remainsconstant, a vapor at saturation temperature condenses into its liquidphase as thermal energy is removed. The saturation temperature can beincreased by increasing the pressure in the system. Conversely, thesaturation temperature can be decreased by decreasing the pressure inthe system. In specific versions of the invention, a saturationtemperature “slightly above” the temperature of jet streams 16 ofcoolant projected at the surface to be cooled 12 refers to a saturationtemperature of about 0.5° C., about 1° C., about 3° C., about 5° C.,about 7° C., about 10° C., about 15° C., about 20° C., or about 30° C.above the temperature of coolant 50 projected against the surface.Establishing a saturation temperature of coolant 50 surrounding asurface 12 slightly above the temperature of the jet stream 16 ofcoolant projected at the surface provides for at least a portion of thecoolant projected at the surface to heat and evaporate after contactingthe surface, thereby greatly increasing the heat transfer rate andefficiency of the cooling apparatus 1.

The appropriate pressure at which to maintain the coolant to achieve thepreferred saturation temperatures can be determined theoretically byrearranging the following Clausius-Clapeyron equation to solve for P₀:

$T_{B} = \left( {\frac{R\; {\ln \left( P_{0} \right)}}{\Delta \; H_{vaporization}} + \frac{1}{T_{0}}} \right)^{- 1}$

where: T_(B)=normal boiling point (K), R=ideal gas constant(J-K⁻¹mol⁻¹), P₀=vapor pressure at a given temperature (atm),ΔH_(vaporization)=heat of vaporization of the coolant (J/mol), T₀=giventemperature (K), and ln=natural log to the base e.

In the above equation, the given temperature (T₀) is the temperature ofcoolant 50 in contact with, and heated by, the surface to be cooled 12.The normal boiling point (T_(B)) is the boiling point of the coolant ata pressure of one atmosphere. The heat of vaporization(ΔH_(vaporization)) is the amount of energy required to convert orvaporize a given quantity of a saturated liquid (i.e., a liquid at itsboiling point) into a vapor. As an alternative to determining theappropriate pressure theoretically, the appropriate pressure can bedetermined empirically by adjusting the pressure and detectingevaporation or bubble generation at a surface to be cooled 12, as shownin FIG. 30. Bubble generation can be visually detected with a human eyewhen transparent components, such as a transparent heat sink module 100or transparent flexible tubing 225, is used to construct the coolingapparatus 1. In some examples, the heat sink module 100 or the flexibletubing 225 can be transparent throughout, and in other examples, atleast a portion of the heat sink module 100 or flexible tubing 225 canbe transparent to provide a transparent window portion that permits asystem operator or electronic eye to visually detect the presence ofbubbles 275 within the coolant 50 flow and to make system adjustmentsbased on that visual detection. For instance, if no bubbles 275 arevisually detected exiting the outlet chamber 150 of the heat sink module100, the coolant flow rate can be reduced by reducing the pump 20 speed,thereby reducing energy consumed by the pump 20 and reducing overallenergy consumption and operating cost. Conversely, if slug or churn flowis detected (see, e.g. FIGS. 58 and 59B), the coolant flow rate 51 canbe increased to eliminate the presence of those unwanted flow regimesand restore the system to two-phase bubbly flow.

During operation of the cooling apparatus 1, coolant 50 can be flowedinto an outlet chamber 150 of the heat sink module 100. The surface tobe cooled 12 can be exposed within the outlet chamber 150 or, as shownin FIG. 30, the surface to be cooled 12 can serve as a bounding surfaceof the outlet chamber 150 when the heat sink module 100 is installed onthe surface to be cooled 12. The coolant 50 can be introduced to theoutlet chamber 150 at a predetermined pressure that promotes a phasechange upon the liquid coolant 50 contacting, and being heated by, thesurface to be cooled 12. One example of such a cooling apparatus 1 forperforming various cooling methods described herein is shown in FIG.11A. The cooling apparatus 1 can include a heat sink module 100, asshown in FIGS. 26 and 30. The heat sink module 100 can include an outletchamber 150 with a surface 12 to be cooled exposed within the outletchamber 150. The pump 20, as shown in FIG. 11A, can provide coolant 50at a predetermined pressure to an inlet 21 of the heat sink module 100.

The cooling apparatus 1 as described above and as shown in FIG. 11A caninclude several steady-state zones having either liquid flow ortwo-phase bubbly flow. The nature of the coolant 50 in each zone candepend on the temperature and pressure of the coolant in each zone. Inthe example in FIG. 11A, a zone having high-temperature coolant 52includes the coolant 50 surrounding the surface to be cooled 12 withinthe outlet chamber 150 (excluding the jet streams 16 of coolant 50projected into the outlet chamber 150 through the orifices 155 of theheat sink module 100) of the heat sink module 100 and extends downstreamto the heat exchanger 40 (see FIG. 11A for direction of flow 51).Portions of the high-temperature coolant 52 within the outlet chamber150 are preferably at a temperature approximately equal to or above thesaturation temperature. A zone of low-temperature coolant 53 extendsfrom downstream of the reservoir 200 to at least the inlet port 105 ofthe first heat sink module 100 and includes the jet streams 16 ofcoolant 50 injected into the outlet chamber 150 of the first heat sinkmodule 100. The low-temperature coolant 53 is preferably at atemperature slightly below the saturation temperature of the coolant 50surrounding the surface 12, wherein “slightly below” can include 0.5-1,0.5-3, 1-3, 1-5, 3-7, 5-10, 7-10, 7-15, 10-15, 15-20, 15-30, about 0.5,about 1, about 3, about 5, about 7, about 10, about 15, about 20, orabout 30° C. or more below the saturation temperature of coolant 50surrounding the surface to be cooled 12. Heat transfer from the surfaceto be cooled 12 to the coolant 50 with the outlet chamber 150 of theheat sink module 100 serves to transition the low-temperature coolant 53to high-temperature coolant 52. In some examples, the surface to becooled 12 heats a portion of the coolant 50 contacting the surface 12 toits saturation temperature, thereby promoting evaporation and formationof two-phase bubbly flow, which exits the heat sink module through theoutlet port 110.

A zone of low-pressure coolant 55 includes the coolant 50 surroundingthe surface to be cooled 12 within the outlet chamber 150 (whichexcludes the jet streams 16 of coolant 50 projecting into the outletchamber 150 through the orifices 155 of the heat sink module) andextends downstream to an inlet 21 of the pump 20. The low-pressurecoolant 55 is preferably at a pressure that promotes evaporation ofcoolant 50 when heated at the surface 12. Therefore, the pressure of thelow-pressure coolant 55 preferably determines a saturation temperatureto be about equal to the temperature of the high-temperature coolant 52.A zone of high-pressure coolant 54 includes a portion downstream of thepump outlet 22 and extends to at least the inlet port 105 of the firstheat sink module 100. The high-pressure coolant 54 is preferably at apressure suitable for generating jet streams 16 of coolant that arecapable of penetrating liquid present in the outlet chamber 150 andimpinging the surface to be cooled 12. In some examples, the pump 20 canprovide high-pressure coolant 54 at a pressure of about 1-20, 10-30,25-50, 40-60, or 50-75, 60-80, or 75-100 psi. In other examples, thepump 20 can provide high-pressure coolant 54 at a pressure of about85-120, 100-140, 130-160, 150-175, 160-185, 175-200, or greater than 200psi.

The pump 20 serves to transition low-pressure coolant 55 tohigh-pressure coolant 54 as the coolant passes from the pump inlet 21 tothe pump outlet 22. In some examples, the pump 20 can providehigh-pressure coolant 54 at a pressure that is about 10-20, 15-30,20-40, 30-45, or 40-60 psi or greater above the pressure of thelow-pressure coolant 55. The high-pressure coolant 54 in the coolingapparatus 1 applies a positive pressure against the plurality oforifices 155 in the heat sink module 100, and the plurality of orifices155 serve to transition the high-pressure coolant 54 to low-pressurecoolant 55, as the coolant 50 equilibrates to the pressure of thelow-pressure coolant 55 after passing through the plurality of orificesas jet streams 16 and mixing with the coolant in the outlet chamber 150of the heat sink module 100.

With the apparatus 1 described above, a flow rate is set by the pump 20to handle the expected heat load produced by the surface to be cooled12. A specific pressure for the low-pressure coolant 55 is set andmaintained by one or more pumps 20 and by one or more pressureregulators 60, as shown in the various schematics presented in FIGS.11A-14, 16-18, and 68-72 to establish a saturation temperature for thecoolant 50 surrounding the surface to be cooled 12 to be slightly abovethe saturation temperature of the low-temperature coolant 53. Relativelyhigh-pressure 54 low-temperature 53 coolant 50 is projected as jetstreams 16 from the plurality of orifices 155 against the surface to becooled 12, whereby the coolant 50 undergoes a pressure drop uponequilibrating with fluid present in the outlet chamber 150 and a portionof the fluid may heat to its saturation temperature upon contacting thesurface 12 and absorbing heat from the surface. A portion of the heatedcoolant 50 undergoes a phase transition at the surface to be cooled 12,which causes highly efficient cooling of the surface 12. Downstream ofthe heat sink module 100, the relatively low-pressure 55,high-temperature 52 coolant flow is then mixed with low-pressure 55,low-temperature 54 coolant from the second bypass 310 to promotecondensing of vapor bubbles 275 within the low-pressure 55, hightemperature 52 coolant by cooling it below its saturation temperature,which produces a flow of low-pressure 55, low-temperature 53 coolant inthe return line 230 that returns the coolant 50 to the reservoir 200.Upon being drawn form the lower portion of the reservoir 200 to the pumpinlet 21, the low-pressure 55, low-temperature 53 coolant is thentransitioned to high-pressure 54, low-temperature 53 coolant as itpasses through the pump 20. The high-pressure 54, low-temperature 53coolant is then circulated back to the inlet port 105 of the first heatsink module 100 and the above-described process is repeated.

Cooling System Preparation and Operation

In some applications, it can be desirable to fill the cooling apparatus1 with a dielectric coolant 50 that is at a pressure below atmosphericpressure (e.g. less than about 14.7 psi). For example, when coolingmicroprocessors 415, it can be desirable fill the cooling apparatus 1with HFE-7000 (or a coolant mixture containing HFE-7000 and, forexample, R-245fa) that is at a pressure below atmospheric pressure toreduce the boiling point of the dielectric fluid. To accomplish this,the portable servicing unit (or other vacuum source) can be used toapply a vacuum to the cooling apparatus 1 to purge the contents of thecooling apparatus. Upon reducing the pressure within the coolingapparatus 1 to about 0-3, 0-5, 1-5, 4-8, 5-10, or 8-14.5 psi, thedielectric coolant 50 can be added to the cooling apparatus 1. In someexamples, operation of the pump 20 may only increase the pressure of thedielectric coolant about 1-15, 5-20, or 10-25 psi above the baselinesub-atmospheric pressure. Consequently, the operating pressure of thehigh pressure coolant 54 within the cooling apparatus 1 may be aboutequal to atmospheric pressure (e.g. about 8-14, 10-16, 12-18, or 14-20psi), thereby ensuring that that saturation temperature of thedielectric coolant remains low enough to ensure that boiling can beachieved when jet streams 16 of coolant impinge the surface to be cooled12 associated with a microprocessor 415. Providing high-pressure coolant54 at a pressure near atmospheric pressure has other added benefits.First, low pressure tubing 225 can be used, which is lightweight,flexible, and low cost. Second, because of the minimal pressuredifference between the high-pressure coolant 54 and the surroundingatmosphere, fluid leakage from fittings and other joints of the coolingapparatus 1 may be less likely.

Temperature Conditioning of Coolant

The cooling apparatus 1 can include any suitable heat exchanger 40configured to promote heat rejection from the flow 51 of coolant toeffectively sub-cool the coolant. By enabling heat rejection from thecoolant 50, the heat exchanger 40 can ensure the reservoir 200 maintainsa volume of subcooled liquid that can be safely supplied to the pump 20without risk of vapor lock or instability. Any heat exchanger 40 capableof reducing the temperature of the coolant 50 below its saturationtemperature is acceptable. For instance, the heat exchanger 40 can beany suitable air-to-liquid heat exchanger or liquid-to-liquid heatexchanger. Non-limiting types of suitable heat exchangers includeshell-and-tube, fin-and-tube, micro-channel, plate, adiabatic-wheel,plate-fin, pillow-plate, fluid, dynamic-scraped-surface, phase-change,direct contact, and spiral type heat exchangers. The heat exchanger 40can operate using parallel flow, counter flow, or a combination thereof.In one example, a liquid-to-liquid heat exchanger 40 can be a StandardXchange Brazepak brazed plate heat exchanger from Xylem, Inc. of RyeBrook, N.Y.

A first liquid-to-liquid heat exchanger 40, as shown in FIGS. 92-95 and97, can be connected to an external heat rejection loop 43, as shown inFIG. 77. The external heat rejection loop 43 can carry a flow ofexternal cooling fluid 42, such as water or a water-glycol mixture. Asecond pump 20 can circulate the flow of external cooling fluid 42through the heat rejection loop 43, as shown in FIG. 77. As the flow ofexternal cooling fluid 42 is circulated through the firstliquid-to-liquid heat exchanger 40, heat can be transferred from theflow 51 of dielectric coolant 50 to the flow of external cooling fluid42, thereby subcooling the flow 51 of dielectric coolant 50 in the firstbypass 305 and heating the flow of external cooling fluid 42. The heatedexternal cooling fluid 42 is then circulated through a secondliquid-to-liquid heat exchanger 40 located outside of the room 425 wherethe cooling apparatus 1 is installed. The second liquid-to-liquid heatexchanger 40 can be connected to a flow of chilled water 46, such as achilled water supply from a building. As the heated external coolingfluid 42 circulates through the second liquid-to-liquid heat exchanger40, heat is transferred from the flow of external cooling fluid 42 tothe flow of chilled water, thereby completing heat rejection from thecooling apparatus 1 to the flow of chilled water by way of the heatrejection loop 43.

A cooling apparatus 1 as shown in FIG. 77 can use HFE-7000 as a primarycoolant 50 circulating through one or more heat sink modules 100, a heatrejection loop 43 circulating a flow of a water-glycol mixture 42 as anexternal cooling fluid to transfer heat from a first heat exchanger 40-1to a second heat exchanger 40-2, and a flow of chilled water 46 from abuilding supply line as a third heat exchange medium to carry heat awayfrom the second heat exchanger 40-2. In one example, during operation,the flow 51-1 of subcooled liquid coolant 50 can be about 25-30 degreesC. and about 10-20 psia at an inlet of the first liquid-to-liquid heatexchanger 40-1 and about 20-25 degrees C. at an outlet of the firstliquid-to-liquid heat exchanger. The liquid in the reservoir 200, whichcan be a subcooled liquid with an average temperature of about 25-30degrees C., which is about 5-10 degrees below the saturation temperatureof HFE-7000 at the operating pressure. Where a high heat load fromheated surface 12 is expected, it can be desirable to further subcoolthe flow 51-2 of liquid coolant delivered to the inlet of the heat sinkmodule 100. For instance, it can be desirable to deliver a flow 51-2 ofsubcooled coolant to the heat sink module that is about 15-25 degreesC., which is about 10-15 degrees below the saturation temperature ofHFE-7000 at the operating pressure. The flow of external cooling fluid42 can be about 10-15 degrees C. at an inlet of the firstliquid-to-liquid heat exchanger 40-1 and about 15-20 degrees C. at anoutlet of the first liquid-to-liquid heat exchanger 40-1. The flow ofchilled water 46 can be about 4-7 degrees C. at an inlet of the secondliquid-to-liquid heat exchanger 40-2 and about 9-12 degrees C. at anoutlet of the second liquid-to-liquid heat exchanger. The flow ofexternal cooling fluid 42 can be about 15-20 degrees at an inlet of thesecond liquid-to-liquid heat exchanger and about 10-15 degrees at anoutlet of the second liquid-to-liquid heat exchanger. These values areprovided as an example of one suitable operating condition and arenon-limiting. The temperatures can vary as flow rates, pressures, andheat loads change or when different coolants 50, external cooling fluids42, heat rejection loop 43 configurations, or system configurations areused.

In another example, a liquid-to-liquid heat exchanger 40 can beconnected to an external heat rejection loop 43, as shown in FIG. 75.The external heat rejection loop 43 can carry a flow of external coolingfluid 42, such as water or a water-glycol mixture. A second pump 20-2can circulate the flow of external cooling fluid 42 through the heatrejection loop 43. As the flow of external cooling fluid 42 iscirculated through the first liquid-to-liquid heat exchanger 40-1, heatcan be transferred from the flow 51-1 of dielectric coolant 50 to theflow of external cooling fluid 42, thereby subcooling the flow 51-1 ofdielectric coolant 50 in the first bypass 305 and heating the flow ofexternal cooling fluid 42. The heated external cooling fluid 42 is thencirculated through an air-to-liquid heat exchanger 40-2 located outsideof the room 425 where the cooling apparatus 1 is installed. Theair-to-liquid heat exchanger 40-2 can be a radiator or a dry coolerhaving one or more fans 26 configured to provide airflow across astructure of the heat exchanger. As the heated external cooling fluid 42circulates through the air-to-liquid heat exchanger 40-2, heat istransferred from the flow of external cooling fluid 42 to the flow ofair, thereby completing heat rejection from the cooling apparatus 1 toambient air by way of the heat rejection loop 43. As shown in FIG. 75,the air-to-liquid heat exchanger 40-2 can be located outside the room425 where the surface to be cooled 12 is located to avoid rejecting theheat to the ambient air in the room 425 and thereby increasing the airtemperature in the room 425.

In some examples, the heat exchanger 40 can be a liquid-to-liquid heatexchanger 40 that is directly connected to a flow of external coolingfluid 46, such as chilled water from a building supply line, as shown inFIG. 76. This configuration can allow heat rejected from the coolingapparatus 1 to be removed from the room 425 where the cooling apparatus1 is installed and transferred directly to a flow of chilled water 46instead of being rejected into the room air or through an intermediateheat rejection loop 43, as shown in FIG. 77. In this example, careshould be taken to regulate the flow rate of chilled water 46 throughthe heat exchanger 40 to avoid cooling the dielectric coolant 50 to atemperature at or below its dew point.

In any of the cooling apparatuses 1 described herein, the flow rate ofcoolant 50-1 through the heat exchanger 40 can be monitored andcontrolled to avoid reducing the temperature of the low-temperature 53coolant to or below the dew point of ambient air in the room 425 wherethe surface to be cooled 12 is located. Reaching or dropping below thedew point of the ambient air is undesirable, since it can causecondensation to form on an outer surface of the flexible tubing 225 orother components of the cooling apparatus 1. If this occurs, waterdroplets can form on and fall from the outer surface of the tubing 225onto sensitive electrical components within the server 400, such as themicroprocessor 415 or memory modules 420, which is undesirable.Consequently, the low-temperature 53 coolant should be maintained at atemperature above the dew point of ambient air in the room 425 to ensurethat condensation will not form on any components of the coolingapparatus 1 that are in close proximity to sensitive electrical devicesbeing cooled.

In some examples, if the low-temperature 53 coolant is cooled below thedew point of ambient air in the room by the heat exchanger 40, apreheater can be provided in line with, or upstream of, the line (e.g.flexible tubing 225) that transports coolant 50 flow into the server 400housing and into the heat sink module 100. The preheater can be used toheat the flow of coolant 51 to bring the coolant temperature above itsdew point temperature, thereby avoiding potential complications causedby condensation forming on the lines within the server housing. In someexamples, the preheater can be configured to operate only when needed,such as when the temperature of the low-temperature coolant drops belowits dew point.

The temperature of the low-temperature coolant 52 can be monitored withone or more temperature sensors positioned in the cooling lines, anddata from the sensors can be input to the controller. For instance, afirst temperature sensor can be positioned upstream of the preheater,and a second temperature sensor can be positioned downstream of thepreheater. When the first temperature sensor detects a coolanttemperature that is below the dew point of ambient air in the room 425,the controller can be configured to activate the preheater to heat thelow-temperature coolant 52 to bring the temperature of thelow-temperature coolant above the dew point of the ambient air in theroom 425. In some examples, the rate of heat addition can be ramped upgradually, and once the temperature detected by the second temperaturesensor is above the dew point of the ambient air, the controller can beconfigured to stop ramping the rate of heat addition and instead holdthe heat addition constant. The controller can continue instructing thepreheater to heat the low-temperature coolant 52 until preheating is nolonger needed. For instance, the controller can continue instructing thepreheater to heat the low-temperature coolant 52 until the temperaturedetected by the first temperature sensor is above the dew point of theambient air.

Although the preheating process described above includes measuring thetemperature of the low-temperature coolant 52 directly, in otherexamples the surface temperature of the outer surface of the tubing(e.g. 225) can be measured instead of measuring the coolant temperaturedirectly. For instance, temperature sensors can be affixed directly tothe outer surface of the tubing (e.g. 225) upstream and downstream ofthe preheater. In some instances, this approach can permit fasterinstallation of the temperature sensors and can reduce the number ofpotential leak points in the cooling apparatus 1. In other examples, acontactless temperature-sensing device, such as an infrared temperaturesensor, can be used to detect the temperature of the coolant or thetemperature of the tubing 225 transporting the coolant.

To ensure the temperature of the low temperature coolant 52 remainsabove the dew point temperature of the ambient air, the flow ratethrough the heat exchanger 40 can be decreased and/or the fan speed of afan 26 mounted on the heat exchanger 40 can be reduced to lower the heatrejection rate from the heat exchanger 40 if a low temperature thresholdis detected in the low-temperature coolant. This step can be takeninstead of, or in conjunction with, using the preheater to avoid dewformation on any components of the cooling apparatus 1.

In some examples, the heat exchanger 40 can be upstream of the pressureregulator 60 in the first bypass 305 (see, e.g. FIG. 12A) and in otherexamples, the heat exchanger 40 can be downstream of the pressureregulator 60 in the first bypass 305 (see, e.g. FIG. 11A). “Downstream”and “upstream” are used herein in relation to the direction of flow 51of coolant 50 within the cooling apparatus 1. In other examples, theheat exchanger 40 can be located in the second bypass 310 or in theprimary cooling loop 300.

The cooling apparatuses (1, 2) shown in FIGS. 11A-11D, 12A-12Q, 12S, 13,14A, 16-18, and 68-72 may show heat exchangers 40 that appear to bestand-alone heat exchangers. However, in each of these examples, theheat exchanger 40 can be connected to an external heat rejection loop 43that circulates a flow of external cooling fluid 42, such as water or awater-glycol mixture, as shown in FIGS. 75 and 77. The external heatrejection loop 43 can be fluidly connected to the heat exchanger 40 ofthe cooling apparatus (1, 2) and can be configured to transfer heat fromthe dielectric coolant 50 and reject the heat to air or an other fluidoutside the room 425 where the cooling system 1 is installed. Thisallows the cooling apparatus 1 to avoid rejecting the heat into the room425 where the cooling apparatus is installed, which would increase thetemperature of the room air and place a higher load on the room airconditioner. In each example, the external heat rejection loop 43 can beany suitable heat rejection loop 43, such as the heat rejection loopsshown in FIGS. 12R and 75-77. The external heat rejection loop 43 caninclude any suitable external heat exchanger 40, such as aliquid-to-liquid heat exchanger 40-2 as shown in FIG. 77 or anair-to-liquid heat exchanger 40-2 as shown in FIG. 75. Alternately, theheat rejection loop 43 may not include an external heat exchanger, suchas in FIG. 76, where a flow of chilled water 46 from a building isconnected directly to the heat exchanger 40 of the cooling apparatus 1.

Flow within Cooling Apparatus

Flow rates in the cooling apparatus 1 can be adjusted to ensure stabletwo-phase flow within the cooling apparatus 1. More specifically, flowrates within the cooling apparatus 1 can be adjusted to promote reliablecondensing of vapor within a two-phase flow in the cooling apparatus bymixing the two-phase flow (e.g. 51-2) exiting the one or more heat sinkmodules 100 with subcooled liquid flow from the first and/or secondbypass (e.g. 51-1, 51-3), either within the outlet manifold 215, thereturn line 230, and/or the reservoir 200. This approach achievesreliable condensing of vapor upstream of the pump 20 to ensure that onlysingle-phase liquid coolant is provided to the pump inlet 21 and,therefore, the pump 20 is only tasked with pumping single-phase liquidcoolant, which can be pumped more efficiently and reliably thantwo-phase flow.

In some examples, the flow rate 51 of coolant 50 provided by the pump 20in the cooling apparatus 1 can be selected based, at least in part, onthe number of heat sink modules 100 fluidly connected to the primarycooling loop 300. In many instances, a flow rate of about 0.25-5,0.5-1.5, 0.8-1.2, 0.9-1.1, or about 1 liter per minute through each heatsink module 100 can be desirable. For a configuration as shown in FIG.75, where only one heat sink module 100 is provided, the flow of coolant51-2 through the primary cooling loop 300 can be about 1.0 liter perminute in one specific example. The flow rate 51-3 delivered to thesecond bypass 310 can be about equal to the flow rate 51-2 in theprimary cooling loop 300 (i.e. 1.0 liter per minute). The flow rate 51-1in the first bypass 305, which is passed through the heat exchanger40-1, can be about equal to the sum of the flow rate 51-2 in the primarycooling loop and the flow rate 51-3 in the second bypass 310 (i.e.51-1=51-2+51-3), or about 2.0 liters per minute. Consequently, the totalflow rate 51 provided by the pump 20-1 can be about four times the flowrate 51-2 in the primary cooling loop 300 (i.e. 51=4*51-2). Therefore,the total flow rate 51 provided by the pump 20-1 can be about 4 litersper minute in this specific example. When higher heat loads areencountered, the total flow rate 51 can be increased to ensure flowstability within the cooling apparatus 1.

FIG. 75 shows a basic cooling apparatus 1 having a primary cooling loop300 with a single heat sink module 100. In more complicated coolingapparatuses 1, such as the cooling apparatus 1 shown in FIG. 78, theflow 51-2 delivered to the primary cooling loop 300 can be distributedamong one or more cooling lines 303 extending between an inlet manifold210 and an outlet manifold 215. Consequently, a portion of the primarycooling loop 300 can include a plurality of cooling lines 303 extendingfrom an inlet manifold 210 to an outlet manifold 215.

In FIG. 78, the inlet and outlet manifolds (210, 215) are configured toaccommodate up to twelve cooling lines 303, but only eight cooling linesare shown connected. Consequently, the cooling apparatus 1 in FIG. 78can be expanded during operation of the cooling apparatus 1 to includefour additional cooling lines 303 as additional cooling is required(e.g. as additional servers 400 are added to a rack 410 of servers).Each cooling line 303 can be fluidly connected to the inlet and outletmanifolds (210, 215) using, for example, quick-connect fittings 235.Each cooling line 303 can include one or more heat sink modules 100arranged on heat-providing surfaces 12, such as on microprocessors 415in servers 400. When a new server 400 is added to the server rack 405, anew cooling line 303 can be rapidly connected to the inlet and outletmanifolds (210, 215) using quick-connect fittings 235, and each heatsink module 100 that is fluidly connected to the cooling line 303 can bemounted on a heat-providing surface 12 (e.g. microprocessor, RAM, orpower supply) within the new server 400 to provide efficient, localcooling. This flexible configuration allows the cooling apparatus 1 tobe easily modified to meet the cooling requirements of a growingcollection of servers 400 (e.g. in a computer room 425) by simply addingadditional cooling lines 303 to the existing cooling apparatus 1. Theuse of quick-connect fittings 235 can allow additional cooling lines 303to be added while the cooling apparatus 1 is operating without riskingcoolant leakage or pressure loss. One example of a suitablequick-connect fitting is a NS4 Series coupling available from ColderProducts Company of St. Paul, Minn. The quick-connect fitting 235 caninclude a non-spill valve and can be made of a medical-grade ABSmaterial. The non-spill valve can allow the quick-connect fitting 235 tobe disconnected under pressure without spilling any coolant 50.

In some examples, the flow rate 51 provided by the pump 20-1 can beselected based, at least in part, on the number of cooling lines 303(i.e. maximum number of cooling lines or the actual number of coolinglines 303) extending between the inlet manifold 210 and the outletmanifold 215. For instance, in FIG. 78, the flow rate 51 provided by thepump 20-1 can be selected to accommodate eight eight cooling lines 303extending between the inlet manifold 210 and the outlet manifold 215, orthe flow rate 51 provided by the pump 20-1 can be selected toaccommodate twelve cooling lines 303 extending between the inletmanifold 210 and the outlet manifold 215. Selecting the flow rate 51 toaccommodate the actual number of cooling lines 303 (i.e. eight) canprovide more efficient operation by reducing the flow rate 51 requiredfrom the pump 20-1. Selecting the flow rate 51 to accommodate themaximum number of cooling lines 303 can ensure adequate flow to allow anoperator to connect additional cooling lines 303 without resulting inunstable operation of the cooling apparatus 1. This approach can beuseful for cooling apparatuses 1 that are not equipped with sensors toenable the electronic control system 850 to determine how many coolinglines 303 are connected and to automatically adjust the flow 51 ifcooling lines are added or removed. For cooling apparatuses that areequipped with sensors that allow the electronic control system 850 todetermine how many cooling lines 303 are connected between themanifolds, the pump 20-1 speed can be adjusted to provide a flow rate 51based on the number of detected cooling lines 303. In some examples, thesensors can be flow sensors that detect the presence of flow passingthrough quick connect fitting 235 connected to the manifold. In anotherexample, the sensors can be proximity sensors that detect the presenceof quick connect couplers connected to the manifold.

In FIG. 79, the flow rate 51 provided by the pump 20-1 can be selectedto accommodate thirty cooling lines 303 extending between the inletmanifold 210 and the outlet manifold 215. This configuration can besuitable for cooling thirty servers 400 arranged in close proximity in aserver rack 405. A flow rate of about 1.0 liter per minute can beselected as a suitable flow rate through each cooling line 303. Sincethere are thirty cooling lines 303, a total flow rate through theprimary cooling loop 300 of about 30 liters per minute can be provided.A similar flow rate 51-2 of about 30 liters per minute can be deliveredthrough the second bypass 305, which in the example of FIG. 79 isarranged between the inlet and outlet manifolds (210, 215). The flowrate 51-1 through the first bypass 305 can be about equal to a sum ofthe flow through the primary cooling loop 300 and the flow through thesecond bypass 310 (i.e. 51-1=51-2+51-3). Therefore, the flow rate 51-1through the first bypass can be about 60 liters per minute in thisexample, and the total flow rate 51 provided by the pump 20-1 can beabout 120 liters per minute (51=51-1+51-2+51-3).

In the example shown in FIG. 79, a flow of subcooled liquid coolant 50can be provided to the inlet manifold 210 by the pump 20-1. In someinstances, about half of the flow delivered to the inlet manifold 210can be routed through the pressure regulator 60 in the second bypass310, and the other half of the flow can be routed through the thirtycooling lines 303. To ensure stable operation of the cooling apparatus1, it is preferable to condense the two-phase bubbly flow in the outletmanifold 215 or return line 230 before it returns to the reservoir 200.This reduces the chance of vapor being introduced to the pump 20-1 andcausing vapor lock or flow instabilities. The amount of heat that can beremoved by the cooling apparatus 1 can be defined by the followingequation:

Q _(sensible) ={dot over (m)} _(liquid) ×c _(p) ×ΔT _(subcooled)

where Q_(sensible) is the amount of heat in Watts, {dot over(m)}_(liquid) is the mass flow rate through the cooling lines 303 andthe second bypass 310 (i.e. {dot over(m)}_(liquid)=m_(coolant)×(51-2+51-3)), 51-2 is the flow rate throughall cooling lines 303 in the primary cooling loop 300, 51-3 is the flowrate through the second bypass 310, c_(p) is the specific heat of thecoolant in J/(kg-K), and ΔT_(subcooled) is the difference in degrees C.between the saturation temperature (T_(sat)) of the coolant in the inletmanifold 210 and the actual temperature of the coolant in the inletmanifold (i.e. ΔT_(subcooled)=T_(sat)−T_(inlet manifold)). In oneexample of the apparatus 1 shown in FIG. 79, where the coolant isHFE-7000, the specific heat is about 1300 J/(kg-K) and the mass is about1.4 kg/liter. Altogether, about 30 liters per minute of coolant 50 canbe pumped through the cooling lines 303, resulting in 51-2 equaling 30liters per minute. The flow rate 51-3 being pumped through the secondbypass 310 can be about 30 liters per minute. The total flow rate(51-2+51-3) delivered to the inlet manifold 210 can be about 60 litersper minute, which is equal to about 1.4 kg/sec when the coolant isHFE-7000. The coolant 50 delivered to the inlet manifold 210 can besubcooled about 10 degrees C. below its saturation temperature at theinlet manifold pressure. Based on these conditions, the amount of heat Qthat can be removed by the cooling apparatus in FIG. 79 is about 18,200W. Adding 18,200 watts of heat to the coolant 50 will increase the bulkcoolant temperature to its saturation temperature. It can be desirablenot to exceed this amount of heat, since doing so would not allow forcomplete condensing of the vapor in the outlet manifold 215 or returnline 230 upstream of the reservoir 200. Although condensing can also beaccomplished in the reservoir 200, to provide greater stability, it canbe desirable to achieve condensing upstream of the reservoir 200 toreduce the chance of vapor being drawn from the reservoir into the pump20-1.

Within the cooling apparatus 1, heat can be removed from the pluralityof heated surfaces 12 by vaporizing the coolant 50 within the heat sinkmodules 100. In the example discussed above relating to FIG. 79, beforevaporization can occur, the subcooled coolant that is delivered to thecooling lines 303 must first heat to its saturation temperature viasensible heating. To simplify this calculation, we assume that all ofthe flow 51-2 in the cooling lines 303 is heated to its saturationtemperature before any vaporization occurs. A flow rate of 30 liters perminute corresponds to a mass flow rate ({dot over (m)}_(liquid)) ofabout 0.7 kg/sec when using HFE-7000 as the coolant 50. Using theequation above, the heat (0 required to sensibly heat the subcooledliquid to its saturation temperature is about 9,100 W, where {dot over(m)}_(liquid) is 0.7 kg/sec, ΔT_(subcooled) is 10 degrees C., and c_(p)is 1300 J/(kg-K). Since the total amount of heat that can be removed is18,200 W, and 9,100 W is removed through sensible heating, this leaves9,100 W to be removed through latent heating. Assuming a heat ofvaporization (Δh_(vaporization)) of about 140 kJ/kg for HFE-7000, we canuse the following equation to determine the mass flow rate of vapor thatis generated by absorbing 9,100 W of heat:

Q _(latent) ={dot over (m)} _(vapor) ×Δh _(vaporization)

Where the heat of vaporization is about 140 kJ/kg, providing 9,100 W ofheat to coolant that is already at its saturation temperature willproduce about 0.065 kg/sec of vapor. Where the mass flow rate of vaporis about 0.065 kg/sec and the mass flow rate of liquid is about 0.7kg/sec, an average flow quality (x) of about 9% is established. This issafe and stable flow quality (x) corresponding to bubbly flow and iswell below the transition to slug flow described in FIG. 59B.

In one example, a method of providing stable operation of a coolingapparatus 1 containing two-phase bubbly flow can include providing acooling apparatus having a primary cooling loop 300. The primary coolingloop 300 can include a pump 20-1 configured to provide a flow 51 ofsingle-phase liquid coolant 50 at a pump outlet 22-1, as shown in FIG.81. The flow 51 of single-phase liquid coolant can be a dielectriccoolant 50 such as, for example, HFE-7000, HFE-7100, or R-245fa. Thedielectric coolant 51 can have a boiling point of about 15-35 or 30-65degrees C. at a pressure of 1 atmosphere. The primary cooling loop 300can include a reservoir 200 fluidly connected to the primary coolingloop 300 and located upstream of the pump 20-1 and configured to store asupply of single-phase liquid coolant 50 that can be supplied to aninlet 21-1 of the pump 20-1. The primary cooling loop 300 can includeone or more heat sink modules 100 fluidly connected to the primarycooling loop. Each heat sink module 100 can be configured to mount onand remove heat from a heat-providing surface 12, such as a surfaceassociated with a microprocessor 415 in a personal computer or server400.

The cooling apparatus 1 can include a first bypass 305 having a firstend and a second end, as shown in FIG. 81. The first end of the firstbypass 305 can be fluidly connected to the primary cooling loop 300downstream of the pump outlet 22-1. The second end of the first bypass305 can be fluidly connected to the primary cooling loop 300 at thereservoir 200. The first bypass 305 can include a first heat exchanger40-1 and a first pressure regulator 60-1. The first pressure regulator60-1 can be configured to regulate a first bypass flow 51-1 of the flow51 of single-phase liquid coolant through the first heat exchanger 40-1.The first heat exchanger 40-1 can be configured to subcool the firstbypass flow 51-1 of coolant 50 below a saturation temperature of thecoolant.

The cooling apparatus 1 can include a second bypass 310 having a firstend and a second end, as shown in FIG. 81. The first end of the secondbypass 310 can be fluidly connected to the primary cooling loop 300downstream of the pump outlet 22-1 and downstream of the first end ofthe first bypass 305 and upstream of the one or more heat sink modules100. The second end of the second bypass 310 can be fluidly connected tothe primary cooling loop 300 downstream of the one or more heat sinkmodules 100 and upstream of the reservoir 200. The second bypass 310 caninclude a second pressure regulator 40-2 configured to regulate a secondbypass flow 51-3 of the flow 51 of single-phase liquid coolant throughthe second bypass 310. The second end of the second bypass 310 can befluidly connected to the primary cooling loop 300 upstream of a returnline 230 that transports coolant 50 back to the reservoir 200.

The method can include setting the first pressure regulator 40-1 in thefirst bypass 305 to allow about 30-70% of the flow 51 from the pumpoutlet 22-1 to be pumped through the first bypass as the first bypassflow 51-1. The method can include setting the second pressure regulator40-2 in the second bypass 310 to allow 15-50% of the flow 51 from thepump outlet 22-1 to be pumped through the second bypass 310 as thesecond bypass flow 51-3. A remaining portion 51-2 of the flow 51 ofsingle-phase liquid coolant 50 from the pump outlet 22-1 can be pumpedthrough the one or more heat sink modules 100 and transformed intotwo-phase bubbly flow within the one or more heat sink modules as heatis transferred to the remaining portion 51-2 of the flow from the one ormore heat providing surfaces 12. The method can include mixing thetwo-phase bubbly flow 51-2 with the second bypass flow 51-3 upstream ofthe reservoir 200 to condense vapor bubbles 275 within the two-phasebubbly flow 51-2.

Setting the first pressure regulator 40-1 in the first bypass 305 toallow about 30-70% of the flow 51 from the pump outlet 22-1 to be pumpedthrough the first bypass 305 as the first bypass flow 51-1 can includesetting the first pressure regulator 40-1 in the first bypass 305 toallow about 30-40, 35-45, 40-50, 45-55, 50-60, 55-65, or 60-70% of theflow 51 from the pump outlet 22-1 to be pumped through the first bypass305 as the first bypass flow 51-1. Setting the second pressure regulator40-2 in the second bypass 310 to allow 15-50% of the flow 51 from thepump outlet 22-1 to be pumped through the second bypass 310 as thesecond bypass flow 51-3 can include setting the second pressureregulator 40-2 in the second bypass 310 to allow 15-25, 20-30, 25-35,30-40, or 45-50% of the flow 51 from the pump outlet 22-1 to be pumpedthrough the second bypass 310 as the second bypass flow 51-3.

The primary cooling loop 300 can include an inlet manifold 210 and anoutlet manifold 215 and one or more cooling lines 303 extending betweenthe inlet manifold and the outlet manifold, as shown in FIGS. 79 and 81.The one or more heat sink modules 100 can be fluidly connected to theone or more cooling lines 303. Setting the second pressure regulator40-2 can include setting the second pressure regulator 40-2 to provide aflow rate of about 0.25-1.5, 0.7-1.3, 0.8-1.2, 0.9-1.1, or 1.0 litersper minute of coolant 50 through each of the one or more cooling lines303. Setting the first pressure regulator 40-1 can include establishinga pressure differential of about 5-15 psi between an inlet and an outletof the first pressure regulator 40-1. Likewise, setting the secondpressure regulator 40-2 can include establishing a pressure differentialof about 5-15 psi between an inlet and an outlet of the second pressureregulator 40-2.

In another example, a method can allow cooling lines 303 extending froman inlet manifold 210 to an outlet manifold 215 of an operating coolingapparatus 1, as shown in FIG. 78, to be safely added or removed withoutcausing unstable two-phase flow to develop within the cooling apparatus1. The method can include providing a cooling apparatus 1 with an inletmanifold 210, an outlet manifold 215, a bypass 310 extending from theinlet manifold 210 to the outlet manifold 215, and M connection ports235 on each of the inlet manifold and the outlet manifold to accommodateup to M cooling lines 303 extending between the inlet manifold and theoutlet manifold, where M is a variable. The bypass 310 can include apressure regulator 40-2. The method can include providing a flow rate 51of single-phase liquid coolant 50 to the inlet manifold 210 and settingthe pressure regulator 40-2 in the bypass 310 to provide a flow ratethrough the bypass ({dot over (V)}_(bypass)) 51-3 of about (M×{dot over(V)}_(line))+(M−L)×{dot over (V)}_(line), where {dot over (V)}_(line) isan average flow rate through each of the cooling lines, where L is theactual number of cooling lines 303 installed between the inlet manifoldand the outlet manifold, and L is equal to or less than M. In FIG. 78, Mis twelve, and L is eight. In some examples, {dot over (V)}_(line) canbe about equal to 0.25-1.5, 0.7-1.3, 0.8-1.2, 0.9-1.1, or 1.0 liters perminute of coolant, and M can be 1-10, 5-15, 10-30, 20-40, 30-60, 50-100,75-150, or 120-240. Where more than one set of manifolds are used, M canrepresent the total number of cooling lines that can be accommodated.For example, in FIG. 80, M is equal to 60 where two sets of manifoldsare used and each set can accommodate 30 cooling lines 303.

Providing the flow rate of single-phase liquid coolant 50 to the inletmanifold 210 can include providing a flow rate of single-phase,dielectric coolant including HFE-7000, HFE-7100, or R-245fa. The boilingpoint of the dielectric coolant can be about 15-35 or 30-65 degrees C.at a pressure of 1 atmosphere. Providing the flow rate of single-phaseliquid coolant to the inlet manifold 210 can include providing a flow ofsingle-phase liquid coolant 50 that is subcooled below a saturationtemperature (T_(sat)) of the single-phase liquid coolant. Providing theflow rate of single-phase liquid coolant that is subcooled below asaturation temperature of the single-phase liquid coolant can includeproviding a flow of single-phase liquid coolant 50 that is subcooledabout 2-8, 5-10, or 12-15 degrees C. below the saturation temperature(T_(sat)) of the single-phase liquid coolant. Providing the flow rate ofsingle-phase liquid coolant to the inlet manifold 210 can includeproviding a flow rate of single-phase liquid coolant at a pressure ofabout 5-20, 15-25, or 20-35 psia.

In yet another example, a method of selecting flow rates to providestable operation within a cooling apparatus 1 in which two-phase bubblyflow is present can include providing a cooling apparatus having aprimary cooling loop 300. The primary cooling loop can include a pump20-1 configured to provide a flow rate 51 of single-phase liquid coolantat a pump outlet. The flow rate of single-phase liquid coolant at thepump outlet can be a dielectric coolant such as, for example, HFE-7000,HFE-7100, or R-245fa with a boiling point of about 15-35 or 30-65degrees C. at a pressure of 1 atmosphere. The primary cooling loop 300can include a reservoir 200 fluidly connected to the primary coolingloop 300 and located upstream of the pump 20 and configured to store asupply of single-phase liquid coolant 50 for the pump 20. The primarycooling loop 300 can include one or more cooling lines 303 fluidlyconnected to the primary cooling loop 300 and extending between an inletmanifold 210 and an outlet manifold 215, as shown in FIGS. 75, 79, 80,and 81. Each cooling line 303 can be fluidly connected to one or moreheat sink modules 100, and each heat sink module 100 can be mounted on aheat-providing surface 12, such as a surface associated with amicroprocessor 415, memory module 420, or power supply of a personalcomputer or server 12.

The cooling apparatus 1 can include a first bypass 305 having a firstend and a second end. The first end of the first bypass 305 can befluidly connected to the primary cooling loop 300 downstream of the pumpoutlet 22-1. The second end of the first bypass 305 can be fluidlyconnected to the primary cooling loop 300 upstream of the reservoir 200and downstream of the heat sink modules 100. The first bypass 305 caninclude a first heat exchanger 40-1 and a first pressure regulator 60-1.The first pressure regulator 40-1 can be configured to regulate a firstbypass flow rate 51-1 of the flow rate 51 of single-phase liquid coolant50 through the first heat exchanger 40-1. The first heat exchanger 40-1can be configured to subcool the first bypass flow rate 51-1 of coolant50 below a saturation temperature of the coolant 50.

The cooling apparatus 1 can include a second bypass 310 having a firstend and a second end. The first end of the second bypass 310 can befluidly connected to the primary cooling loop 300 downstream of the pump20, downstream of the first end of the first bypass 305, and upstream ofthe one or more heat sink modules 100. The second end of the secondbypass 310 can be fluidly connected to the primary cooling loop 300downstream of the one or more heat sink modules 100 and upstream of thereservoir 200. The second bypass 310 can include a second pressureregulator 60-2 configured to regulate a second bypass flow rate 51-3 ofthe single-phase liquid coolant 50 through the second bypass 310.

The method can include setting the second pressure regulator 60-2 toprovide a flow rate of about {dot over (V)}_(line) through each of thecooling lines 303 and to provide the second bypass flow rate 51-3 aboutequal to L×{dot over (V)}_(line), where L is the number of cooling lines303 extending between the inlet manifold 210 and the outlet manifold215. The method can include setting the first pressure regulator 60-1 toprovide the first bypass flow rate 51-1 about equal to 2 L×{dot over(V)}_(line) The average flow rate ({dot over (V)}_(line)) of coolantthrough each cooling line 303 can be about equal to 0.25-5, 0.25-1.5,0.7-1.3, 0.8-1.2, 0.9-1.1, or 1.0 liter per minute.

In one example, a method of condensing vapor present in two-phase bubblyflow within a cooling apparatus 1 can include providing a first flow(e.g. 51-2) of coolant including two-phase bubbly flow. The two-phasebubbly flow can include vapor bubbles 275 dispersed in liquid coolant50. The first flow of coolant can have a first flow quality greater thanzero. The method can include providing a second flow (e.g. 51-3) ofcoolant including single-phase liquid flow. The second flow of coolantcan have a second flow quality of about zero. The method can includemixing the first flow of coolant and the second flow of coolant to forma third flow of coolant, as shown in the return line 230 in FIG. 81.Mixing the first flow of coolant and the second flow of coolant cancause heat transfer from the first flow of coolant to the second flow ofcoolant and can cause vapor bubbles 275 within first flow of coolant tocondense (e.g. within the return line 230 and/or in the reservoir 200).The third flow of coolant can have a third flow quality less than thefirst flow quality of the first flow of coolant.

Providing the first flow (e.g. 51-2) of coolant can include providing afirst predetermined flow rate (e.g. {dot over (V)}_(line)) of two-phasebubbly flow. Providing the second flow (see, e.g. 51-3 and/or 51-1 inFIG. 81) can include providing a second predetermined flow rate ofsingle-phase liquid flow. The second predetermined flow rate can begreater than or equal to the first predetermined flow rate. The secondpredetermined flow rate can be at least two times greater than the firstpredetermined flow rate. The second predetermined flow rate can be atleast four times greater than the first predetermined flow rate. Thefirst flow quality can be about 0.05-0.10, 0.07-0.15, 0.10-0.20,0.15-0.25, 0.2-0.4, or 0.3-0.45. The second flow quality can be aboutzero. The third flow quality can be about 0-0.05, 0.04-0.1, 0.08-0.15,or 0.1-0.2. The first predetermined flow rate can be about 0.1-10,0.2-5, 0.3-2.5, 0.6-1.2, or 0.8-1.1 liters per minute. Providing thefirst flow of coolant can include providing the first flow of coolantfrom a primary cooling line 303 including a heat sink module 100 fluidlyconnected to the primary cooling line 303. The heat sink module 100 canbe configured to mount on a heat-providing surface 12. Providing thesecond flow of coolant can include providing the second flow of coolantfrom a bypass. The bypass (e.g. 310) can include a pressure regulator 60configured to control a flow rate of the second flow of coolant throughthe bypass.

In another example, a method of condensing vapor in two-phase bubblyflow in a cooling apparatus 1 can include providing a first flow (e.g.51-2) of coolant including two-phase bubbly flow, as shown in thesection of tubing 225 connected to the outlet port 110 of the heat sinkmodule 100 in FIG. 81. The two-phase bubbly flow can include liquidcoolant and a plurality of vapor bubbles 275 of coolant suspended in theliquid coolant. The first flow can have a first flow quality. The firstflow can have a first predetermined pressure of about 10-20, 15-25, or20-30 psia and a first temperature about equal to a saturationtemperature of the first flow of coolant at the first predeterminedpressure. The method can include providing a second flow (e.g. 51-3) ofcoolant including single-phase liquid flow having a second flow quality.The second flow can have a second predetermined pressure of about 10-20,15-25, or 20-30 psia and a temperature below the saturation temperatureof the second flow of coolant at the second predetermined pressure. Themethod can include mixing the first flow and the second flow to form athird flow of coolant having a third flow quality. The third flowquality can be less than the first flow quality of the first flow.

Providing the first flow (e.g. 51-2) can include providing a firstpredetermined flow rate (e.g. {dot over (V)}_(line)) of two-phase bubblyflow. Providing the second flow (e.g. 51-3) can include providing asecond predetermined flow rate of single-phase flow. The secondpredetermined flow rate can be greater than or equal to the firstpredetermined flow rate. The second predetermined flow rate can be atleast two times greater than the first predetermined flow rate. Thesecond predetermined flow rate can be at least four times greater thanthe first predetermined flow rate. The first flow quality can be about0.05-0.10, 0.07-0.15, 0.10-0.20, 0.15-0.25, 0.2-0.4, or 0.3-0.45. Thesecond flow quality can be about zero. The third flow quality can beabout 0-1, 0-0.5, 0-0.25, 0-0.2, 0-.05, 0-0.02, or 0-0.1. The firstpredetermined flow rate (e.g. {dot over (V)}_(line)) can be about0.1-10, 0.2-5, 0.3-2.5, 0.6-1.2, or 0.8-1.1 liters per minute. Mixingthe first flow with the second flow to form the third flow can result incondensing of at least a portion of the plurality of vapor bubbles 275from the first flow as heat is transferred from the first flow to thesecond flow. The first flow can include a dielectric coolant includingR-245fa, HFE-7000, or HFE-7100.

In yet another example, a method of condensing vapor in two-phase bubblyflow in a cooling apparatus 1 can include providing a cooling apparatushaving an inlet manifold 210, an outlet manifold 215, a cooling line 303extending from the inlet manifold to the outlet manifold, and a bypass310 extending from the inlet manifold to the outlet manifold, as shownin FIG. 79. The cooling line 303 can be fluidly connected to a heat sinkmodule 100 that is mounted on a heat-providing surface 12. The methodcan include providing a flow of single-phase liquid coolant to the inletmanifold. The method can include flowing a first flow portion of theflow of single-phase liquid coolant through the cooling line 303 fromthe inlet manifold 210 to the outlet manifold 215. The first flowportion can pass through the heat sink module 100 and can absorb asufficient amount of heat from the heat-providing surface 12 to cause afraction of the first flow portion to change phase from liquid to avapor thereby forming a two-phase bubbly flow of coolant. The method caninclude flowing a second flow portion of the flow of single-phase liquidcoolant through the bypass line 310 from the inlet manifold 210 to theoutlet manifold 215. The method can include mixing the first flowportion and the second flow portion in the outlet manifold 215 to form amixed flow. Mixing the first and second flow portions can cause heattransfer from the first flow portion to the second flow portion therebycondensing at least a portion of the vapor from the first flow portion.Flowing the first flow portion of the flow of single-phase liquidcoolant through the cooling line 303 can include flowing a first flowrate of about 0.1-10, 0.2-5, 0.3-2.5, 0.6-1.2, or 0.8-1.1 liters perminute of coolant through the first cooling line 303. Flowing the secondflow portion of the flow of single-phase liquid coolant through thebypass line 310 can include flowing a second flow rate through thebypass. The second flow rate can be greater than or equal to the firstflow rate.

In one example, a method of providing a continuous flow of single-phaseliquid to a pump 20 in a cooling apparatus 1, in which two-phase flow ispresent but is condensed upstream of the pump 20 to provide stable pumpoperation, can include providing a cooling apparatus 1 having areservoir 200 fluidly connected to a pump 20. The reservoir 200 can beconfigured to store an amount of coolant 50, such as a dielectriccoolant. The reservoir 200 can have a liquid-vapor interface 202 in anupper portion of the reservoir when partially filled with liquidcoolant. The liquid-vapor interface 202 can be an interface locatedbetween an amount of substantially liquid coolant 50 and an amount ofsubstantially vapor coolant, as shown in FIGS. 81-83. The method caninclude delivering an inlet flow of single-phase liquid coolant to thereservoir 200. The method can include delivering two-phase bubbly flowto an upper portion of the reservoir 200 above the liquid-vaporinterface 202. The two-phase bubbly flow of coolant can include vaporbubbles of coolant dispersed in liquid coolant. The vapor bubbles 275can condense upon interacting with and transferring heat to the amountof liquid coolant 50 in the reservoir 200. The method can includedelivering a continuous outlet flow of single-phase liquid from a lowerportion of the reservoir 200 to a pump 20 to provide stable pumpoperation. The lower portion can be located below a midpoint of thereservoir 200, and in some cases can be located at a bottom surface ofthe reservoir 200 as shown in FIGS. 81-83.

The inlet flow of single-phase liquid coolant can have a first flowrate, and the two-phase bubbly flow can have a second flow rate. Thefirst flow rate can be equal to or greater than the second flow rate.The amount of liquid coolant in the reservoir 200 can occupy about50-90, 60-80, or 65-75 percent of an interior volume of the reservoir.The flow of single-phase liquid coolant to reservoir can includeproviding a flow of single-phase liquid coolant that is subcooled belowits saturation temperature. Providing the flow of single-phase liquidcoolant that is subcooled below its saturation temperature can includeproviding a flow of single-phase liquid coolant that is subcooled about2-8, 5-12, or 10-15 degrees C. below its saturation temperature.Providing the flow of single-phase liquid coolant to the reservoir caninclude providing a flow of single-phase liquid coolant at a pressure ofabout 10-20, 15-25, 20-30, or 25-40 psia. Providing the flow ofsingle-phase liquid coolant to the reservoir can include providing aflow of single-phase coolant including a dielectric coolant with aboiling point of about 10-35, 20-45, 30-55, or 40-65 degrees C., wherethe boiling point is determined at a pressure of 1 atmosphere.

In another example, a method of providing stable operation of a pump 20in a two-phase cooling apparatus 1 by condensing a two-phase flowupstream of the pump 20 and providing substantially single-phase liquidcoolant to the pump 20 to ensure stable pump operation can includeproviding a first flow of coolant having a two-phase bubbly flow ofcoolant. The two-phase bubbly flow of coolant can include vapor bubbles275 of coolant dispersed in liquid coolant. The first flow of coolantcan have a first flow quality greater than zero. The method can includeproviding a second flow of coolant being a single-phase flow of coolant.The second flow of coolant can have a second flow quality of about zero.The method can include mixing the first flow of coolant (e.g. 51-2) andthe second flow of coolant (e.g. 51-3) to form a return flow of coolant,as shown in FIGS. 81 and 82. Mixing the first flow of coolant and thesecond flow of coolant can cause heat transfer from the first flow ofcoolant to the second flow of coolant and can cause at least a portionof the vapor bubbles 275 of coolant within first flow of coolant tocondense. The return flow of coolant can have a return flow quality thatis less than the first flow quality of the first flow of coolant. Themethod can include delivering the return flow of coolant to a reservoir200. The reservoir 200 can contain a supply of subcooled single-phaseliquid coolant. Mixing the return flow with the supply of subcooledsingle-phase liquid coolant can cause heat transfer from the return flowto the supply of subcooled single-phase liquid coolant therebycondensing any remaining vapor bubbles in the return flow. The methodcan include providing an outlet flow of subcooled single-phase liquidcoolant from the reservoir 200 to a pump 20 to ensure stable pumpoperation. The method can include delivering a third flow (e.g. 51-1) ofcoolant to the reservoir 200, as shown in FIG. 81. The third flow ofcoolant (e.g. 51-1) can be a single-phase flow of coolant. The thirdflow of coolant can pass through a heat exchanger (e.g. 40-1) and besubcooled to about 10-15, 12-20, or 15-30 degrees C. below itssaturation temperature before being delivered to the reservoir 200.

Providing the outlet flow of subcooled single-phase liquid coolant fromthe reservoir 200 to the pump 20 can include providing a flow ofsingle-phase liquid coolant that is subcooled about 2-8, 5-12, or 10-15degrees C. below its saturation temperature. Delivering the return flowof coolant to the reservoir 200 can include delivering the return flowof coolant to an upper portion of the reservoir 200 above a liquid-vaporinterface 202 in the reservoir. The liquid-vapor interface can separatean amount of substantially liquid coolant 50 from an amount ofsubstantially vapor coolant 203. The first flow quality of the firstflow of coolant can be greater than zero and less than about 0.2, 0.25,0.3, 0.35, 0.4, 0.45, or 0.5. The reservoir 200 can be in thermalcommunication with a heat exchanger 40, as shown in FIG. 82. The heatexchanger 40 can be configured to circulate a chilled fluid (e.g. awater-glycol mixture) through sealed passageways (e.g. copper tubingextending into the reservoir or in thermal contact with a sidewall ofthe reservoir) that serves to subcool coolant within the reservoir 200to about 2-8, 5-12, or 10-15 degrees C. below its saturationtemperature. Delivering the return flow of coolant to the reservoir caninclude directing the return flow of coolant against an inner surface ofthe reservoir 200 to promote condensing of the vapor bubbles 275 in thereturn flow of coolant.

In yet another example, a method of providing stable operation of a pump20 in a two-phase cooling apparatus 1 by condensing a two-phase flowupstream of the pump 20 and providing substantially single-phase liquidcoolant to the pump 20 to ensure stable pump operation can includeproviding a cooling apparatus 1. The cooling apparatus 1 can include aninlet manifold 210, an outlet manifold 215, a cooling line 303 extendingfrom the inlet manifold to the outlet manifold, and a bypass 310extending from the inlet manifold 210 to the outlet manifold 215, asshown in FIGS. 79 and 81. The cooling line 303 can be fluidly connectedto a heat sink module 100 that is mounted on a heat-providing surface.The method can include providing a flow of single-phase liquid coolantto the inlet manifold. The method can include flowing a first flowportion (e.g. {dot over (V)}_(line)) of the flow of single-phase liquidcoolant through the cooling line 303 from the inlet manifold 210 to theoutlet manifold 215. The first flow portion (e.g. {dot over (V)}_(line))can pass through the heat sink module 100 and absorb a sufficient amountof heat from the heat-providing surface 12 to cause a fraction of thefirst flow portion to change phase from a liquid to a vapor therebyforming a two-phase bubbly flow of coolant. The method can includeflowing a second flow portion (e.g. 51-2) of the flow of single-phaseliquid coolant through the bypass 310 from the inlet manifold 210 to theoutlet manifold 215. The method can include mixing the first flowportion (e.g. {dot over (V)}_(line)) and the second flow portion (e.g.51-2) in the outlet manifold 210 to form a mixed flow. Mixing the firstand second flow portions can cause heat transfer from the first flowportion to the second flow portion thereby condensing at least a portionof the vapor 275 from the first flow portion. The method can includedelivering the mixed flow to a reservoir 200 containing a supply ofsubcooled liquid coolant 50 where any remaining vapor 275 from the mixedflow is condensed to liquid. The method can include providing an outletflow of substantially liquid coolant from a lower portion of thereservoir 200 to a pump 20 to provide stable pump operation.

Flowing the first flow portion of the flow of single-phase liquidcoolant through the cooling line 303 can include flowing a first flowrate of about 0.1-10, 0.2-5, 0.3-2.5, 0.6-1.2, or 0.8-1.1 liters perminute of coolant through the cooling line 303. Flowing the second flowportion of the flow of single-phase liquid coolant through the bypass310 can include flowing a second flow rate through the bypass. Thesecond flow rate can be greater than or equal to the first flow rate.Providing the flow of single-phase liquid coolant to the inlet manifold210 can include providing a flow of single-phase liquid coolant that issubcooled about 2-8, 5-10, or 12-15 degrees C. below its saturationtemperature. Providing the flow of single-phase liquid coolant to theinlet manifold can include providing a flow of single-phase liquidcoolant at a pressure of about 10-20, 15-25, 20-30, or 25-45 psia.Providing the flow of single-phase liquid coolant to the inlet manifold210 can include providing a flow of single-phase dielectric coolant,such as HFE-7000, HFE-7100, or R-245fa. The method can include routing athird flow portion (e.g. 51-1) of the flow of single-phase liquidcoolant from the reservoir 200 through a heat exchanger 40-1 and back tothe reservoir 200 to provide a flow of subcooled single-phase liquidcoolant to the reservoir, as shown in FIGS. 79 and 81. The third flowportion can be subcooled about 10-15, 12-20, or 15-30 degrees C. belowits saturation temperature upon exiting the heat exchanger and returningto the reservoir.

Cooling Apparatus with Dry Cooler

FIG. 12P shows a schematic of a cooling apparatus 1 having a primarycooling loop 300, a first bypass 305, and a second bypass 310, where thefirst bypass 305 is connected to a heat exchanger 40 that can be arooftop dry cooler. The cooling apparatus 1 can include an electroniccontrol system 850 having a microcontroller that receives inputs fromsensors regarding flow rate, pressure, and temperature and determinesheat removed (W), rate of heat removed (kW-h over time), and pump 20power consumption. The cooling apparatus 1 can include two pumps 20arranged in a parallel configuration for redundancy. Shut-off valves 250can be provided near each pump inlet 21 and outlet 22, thereby allowingfor hot-swapping of a failed pump 20. The shut-off valves 250 can beelectronically controlled by the electronic control system 850 ormanually controlled, depending on the complexity of the coolingapparatus 1. Where the shut-off valves 250 are electronicallycontrolled, a motor fail-safe 855 (see, e.g. FIG. 12P) can be providedto monitor the status of the pumps 20, and in case of pump failure, candeactivate the failed pump and activate the non-failed pump to ensurecontinued flow of coolant through the primary cooling loop 300 to thesurface to be cooled 12. In some examples, the cooling apparatus 1 caninclude a strainer 260 downstream of the pumps 20 and a filter 260upstream of the pumps 20. In some examples, the pressure regulator 60located between the heat exchanger 40 and the reservoir 200 can be aback-pressure valve, such as a liquid relief valve manufactured byKunkle Valve and available from Pentair, Ltd. of Minneapolis, Minn. Insome examples, the pressure regulator 60 positioned in the first bypass305 can be a back pressure valve, such as a liquid relief valvemanufactured by Cash Valve, also available from Pentair, Ltd.

Electronic Control System

The cooling apparatus 1 can include an electronic control system 850, asshown in FIG. 12Q, to enhance performance and reduce power consumptionof the cooling apparatus 1. In some examples, the electronic controlsystem 850 can include a microcontroller. The microcontroller can beelectrically connected to one or more system components, such as a heatexchanger fan 26, a pressure regulator 60, a shut-off valve, or a pump20, and can be configured to dynamically adjust settings of the one ormore components within the cooling apparatus 1 during operation of thecooing apparatus to enhance performance and/or reduce overall powerconsumption. In one example, the microcontroller can be electricallyconnected to a variable speed drive for the pump 20. The microcontrollerand the variable speed drive can allow the pump 20 to operate at a lowerpower when the thermal load from the heat-providing surfaces 12decreases. For instance, the operating pressure at the pump outlet 22can be decreased when the thermal load falls, thereby decreasing theflow rate through the cooling apparatus 1 and the heat sink modules 100fluidly connected thereto. The ability to operate the variable speeddrive at a lower power conserves energy, and is therefore desirable.Where the cooling apparatus 1 includes independent redundant coolingloops, the electronic control system 850 can be configured to operate afirst cooling loop while a second cooling loop is on standby. In someexamples, the electronic control system 850 can be configured toactivate the second cooling loop only if the first cooling loopexperiences a malfunction or is otherwise unable to effectively cool thesurface to be cooled 12. In this way, the redundant cooling apparatus 1can reduce power consumption by about 50% compared to a redundantcooling apparatus where both cooling loops operate continuously.

When a redundant cooling apparatus is provided, the apparatus may runfor long periods of time (e.g. years) without experiencing anymalfunctions or component failures. Consequently, during these longperiods of time, only one cooling loop will be needed and the othercooling loop will remain on standby. To ensure that each cooling loopremains functional and ready to operate when needed, the electroniccontrol system 850 can alternate between operating the first coolingloop and the second cooling loop when only one cooling loop is needed.For instance, the control system can be configured to activate the firstcooling loop for a certain period of time (e.g. a number of hours ordays) while the second cooling loop remains on standby. Once the certainperiod of time has passed, the electronic control system 850 can thenactivate the second cooling loop, and once the second cooling loop isoperating as desired, can place the first cooling loop on standby.Cycling between operating the first cooling loop and operating thesecond cooling loop can extend the life of certain system componentswithin each loop (e.g. pump seals) and can increase the likelihood thatthe standby loop is ready for operation if the other cooling loopexperiences a malfunction. Cycling between the first and second coolingloops can also ensure that operating time is equally distributed betweenthe two cooling loops, thereby potentially increasing the overall usefullife of the redundant cooling apparatus 1.

The cooling apparatus 1 can include one or more sensors that deliverdata to the electronic control system 850 to allow a malfunction withinthe cooling apparatus 1 to be detected and communicated to an operator.The cooling apparatus can include one or more temperature sensors,pressure sensors, visual flow sensors, flow quality sensors, vibrationsensors, smoke detectors, flow rate sensors, fluorocarbon detectors, orleak detectors that deliver data to the electronic control system 850.Each sensor can be electrically connected or wirelessly connected to theelectronic control system 850. Upon detection of a malfunction withinthe cooling apparatus 1, the electronic control system 850 can beconfigured to notify a system operator, for example, with a visual oraudible alarm. The electronic control system 850 can be configured tosend an electronic message (e.g. an email or text message) to a systemoperator to alert the operator of the malfunction. The electronicmessage can include specific details associated with the malfunction,including data recorded from the one or more sensors connected to theelectronic control system 850. The electronic message can also include apart number associated with the component that has likely failed topermit the operator to immediately determine if the part exists in localinventory, and if not, to order a replacement part from a vendor as soonas possible. The electronic message, and any data relating to themalfunction, can be stored in a computer readable medium and/ortransmitted to the system manufacturer for quality control, warranty,and/or recall purposes.

Portable Cooling Device

FIG. 74 shows a portable cooling device 750 that includes a plurality ofheat sink modules 100 mounted on a portable layer 755. In some examples,the portable layer 755 can be a rigid material, such as metal, carbonfiber composite, or plastic. In other examples, the portable layer 755can be a conformable material, such as fabric, foam, or an insulatingblanket. The portable layer 755 can be contoured to correspond to anyheated surface 12. The plurality of heat sink modules (100, 700) can beattached to the portable layer 755 by any suitable method of adhesion.The heat sink modules (100, 700) can be fluidly connected in seriesand/or parallel configurations. The portable cooling device 750 caninclude one or more inlet connections 236 and one or more outletconnections 237 that can be connected to a cooling apparatus 1 thatdelivers a flow of pressurized coolant 50 to the portable cooling device750 to permit cooling of the heated surface 12 through sensible andlatent heating of the coolant within the plurality of heat sink modules.In some examples, each heat sink module can be mounted on a thermallyconductive base member 430. Where the portable layer 755 is made from aninsulated blanket or other insulating member, the portable coolingdevice 750 can be wrapped around a vessel to cool the vessel and itscontents. In this example, the portable layer 755 can include suitablefastening devices (e.g. snaps, ties, zippers, Velcro, or magnets) toallow the portable cooling device to be removably attachable to thevessel.

Heat Pipe

In some examples, a heat pipe can be used as the thermally conductivebase member 430. The heat pipe can include a sealed casing and a wick, avapor cavity, and a working fluid within the sealed casing. In someexamples, the working fluid can be R134a. During a thermal cycle of theheat pipe, the working fluid evaporates to vapor as it absorbs thermalenergy (e.g. from a microprocessor 415 in a server 400). The vapor thenmigrates along the vapor cavity from a first end of the heat pipe towarda second end of the heat pipe, where the second end is at a lowertemperature than the first end. As the vapor migrates toward the secondend of the heat pipe, it cools and condenses back to fluid, which isabsorbed by the wick. The fluid in the wick then flows back to the firstend of the heat pipe due to gravity or capillary action. The thermalcycle then repeats itself.

In some cooling applications, size, shape, or environmental constraintsmay prevent a heat sink module 100 from being placed directly on acomponent or device that requires cooling. In these examples, a heatpipe can be used to transfer heat from the component or device to theheat sink module 100 located at a distance from the component or device.For instance, a first portion of the heat pipe can be placed in thermalcommunication with a heat-providing surface, and the heat sink module100 can be placed in thermal communication with a second portion of theheat pipe, where the second portion is a distance from the firstportion. This approach can allow the heat sink module 100 to efficientlyabsorb heat from the heat-providing surface without being in directcontact or near the heat-providing surface.

By using one or more heat pipes, a single heat sink module (100, 700)can be used to cool two or more heat sources. In one example, a server400 can have two microprocessors 415. A first heat pipe can have a firstend in thermal communication with a first microprocessor 415 and asecond end in thermal communication with a copper base plate 430. Asecond heat pipe can have a first end in thermal communication with asecond microprocessor 415 and a second end in thermal communication withthe same copper base plate 430. A heat sink module (100, 700) can bemounted on a surface to be cooled 12 of the copper base plate 430. Bycirculating a flow of coolant 50 through the heat sink module, andcausing jet streams 16 of coolant to impinge the surface to be cooled ofthe copper base plate 430, the coolant 50 can effectively absorb heatoriginating from the microprocessors 415 that was transferred throughthe heat pipes to the thermally conductive base member 430.

The heat pipe can be any suitable heat pipe, such as a heat pipeavailable from Advanced Cooling Technologies, Inc. located in Lancaster,Pa.

Examples of Heat Sinks

In one example, a heat sink module 100 for cooling a heat providingsurface 12 can include an inlet chamber formed 145 within the heat sinkmodule and an outlet chamber 150 formed within the heat sink module. Theoutlet chamber 150 can have an open portion, such as an open surface.The open portion can be enclosed by the heat providing surface 12 toform a sealed chamber when the heat sink module 100 is installed on theheat providing surface 12, as shown in FIG. 26. The heat sink module 100can include a dividing member 195 disposed between the inlet chamber 145and the outlet chamber 150. The dividing member 195 can include a firstplurality of orifices 155 formed in the dividing member. The firstplurality of orifices 155 can extend from a top surface of the dividingmember 195 to a bottom surface of the dividing member 195. The firstplurality of orifices 155 can be configured to deliver a plurality ofjet streams 16 of coolant 50 into the outlet chamber 150 and against theheat-providing surface 12 when the heat sink module 100 is installed onthe heat providing surface 12 and when pressurized coolant 50 isdelivered to the inlet chamber 145.

A distance between the bottom surface of the dividing member 195 and theheat providing surface 12 can define a jet height 18 of the plurality oforifices 155 when the heat sink module 100 is installed on the heatproviding surface 12. The jet height 18 can be about 0.01-0.75,0.05-0.5, 0.05-0.25, 0.020-0.25, 0.03-0.125, or 0.04-0.08 in.

The first plurality of orifices 155 can have an average diameter ofabout 0.001-0.020, 0.001-0.2, 0.001-0.150, 0.001-0.120, 0.001-0.005, or0.030-0.050 in. The first plurality of orifices 155 can have an averagediameter of D and an average length of L, and L divided by D can begreater than or equal to one or about 1-10, 1-8, 1-6, 1-4, or 1-3.

The dividing member can have a thickness of about 0.005-0.25, 0.020-0.1,0.025-0.08, 0.025-0.075, 0.040-0.070, 0.1-0.25, or 0.040-0.070 in. Eachorifice of the first plurality of orifices 155 can have a central axis,and the central axes of the first plurality of orifices 155 can bearranged at an angle of about 20-80, 30-60, 40-50, or 45 degrees withrespect to the surface to be cooled 12.

The first plurality of orifices 155 can be arranged in an array 76, andthe array can be organized into staggered columns 77 and staggered rows78, as shown in FIG. 31, such that a given orifice 155 in a given column77 and a given row 78 does not have a corresponding orifice 155 in aneighboring row 78 in the given column 77 or a corresponding orifice ina neighboring column 77 in the given row 78.

The heat sink module 100 can include a second plurality of orifices 156extending from the inlet chamber 145 to a rear wall of the outletchamber 150, as shown in FIG. 38. The second plurality of orifices 156can be configured to deliver a plurality of anti-pooling jet streams ofcoolant 16 to a rear portion of the outlet chamber 150 when pressurizedcoolant is provided to the inlet chamber 145. Each orifice of the secondplurality of orifices can have a central axis, where the central axes ofthe second plurality of orifices are arranged at an angle of about40-80, 50-70, or 60 degrees with respect to the surface to be cooled.The second plurality of orifices 156 can be arranged in a column alongthe rear wall of the outlet chamber 150.

The heat sink module 100 can include one or more boiling-inducingmembers 196 extending from the bottom side of the dividing member 195toward the heat providing surface, wherein the one or moreboiling-inducing members 196 are slender members extending from thebottom surface of the dividing member 195. In one example, the one ormore boiling-inducing members 196 can be configured to contact the heatproviding surface 12. In another example, the one or moreboiling-inducing members 196 can be configured to extend toward the heatproviding surface 12, but not contact the heat providing surface 12.Instead, a clearance distance can be provided between the ends of theone or more boiling-inducing members 196 and heat providing surface. Theclearance distance can be about 0.001-0.0125, 0.001-0.05, 0.001-0.02,0.001-0.01, or 0.005-0.010 in.

The inlet chamber 145 of the heat sink module 100 can decrease incross-sectional area in a direction from a front surface 175 of the heatsink module toward a rear surface 180 of the heat sink module, as shownin FIG. 26. The outlet chamber 150 of the heat sink module 100 canincrease in cross-sectional area in a direction from a front surface 170of the heat sink module toward a rear surface 180 of the heat sinkmodule.

The heat sink module 100 can include an inlet port 105 and an inletpassage 165 fluidly connecting the inlet port 105 to the inlet chamber145. The heat sink module 100 can include an outlet port 110 an outletpassage 166 fluidly connecting the outlet chamber 150 to the outlet port110. The heat sink module 100 can include a bottom surface 135 and abottom plane 19 associated with the bottom surface, as shown in FIG. 26.The inlet port 105 can have a central axis 23 that defines an angle (a)of about 10-80, 20-70, 30-60, or 40-50 degrees with respect to thebottom plane 19 of the heat sink module 100. Similarly, the outlet port110 can have a central axis that defines an angle of about 10-80, 20-70,30-60, or 40-50 degrees with respect to the bottom plane of the heatsink module.

An additive manufacturing process, such as stereolithography, can beused to manufacture the heat sink module 100. The stereolithographyprocess can include forming layers of material curable in response tosynergistic stimulation adjacent to previously formed layers of materialand successively curing the layers of material by exposing the layers ofmaterial to a pattern of synergistic stimulation corresponding tosuccessive cross-sections of the heat sink module. The material curablein response to synergistic stimulation can be a liquid photopolymer.

In one example, a heat sink can be configured to receive and discharge aflow of pumped coolant, such as pumped coolant 50 circulating through acooling system. The heat sink can include a thermally conductive basemember 430 configured to mount on, or be placed in thermal communicationwith, a heat source. The thermally conductive base member 430 can have athermal conductivity greater than 100, 150, or 200 Btu/(hr-ft-F). Theheat sink can include a heat sink module 100 having a bottom surface 135that is mounted on a top surface of the thermally conductive basemember, as shown in FIG. 38. The heat sink module 100 can include aninlet chamber 145, an outlet chamber 150, and a dividing member 195. Theinlet chamber 145 can be formed within the heat sink module 100. Theoutlet chamber 150 can be formed at least partially within the heat sinkmodule 100. The outlet chamber 150 can include an open portion enclosedby the top surface 12 of the thermally conductive base member 430 whenthe heat sink module is mounted on the top surface 12 of the thermallyconductive base member 430. The dividing member 195 can be locatedbetween the inlet chamber 145 and the outlet chamber 150. The dividingmember 195 can include a first plurality of orifices 155 formed in thedividing member 195 and passing from a top side of the dividing memberto a bottom side of the dividing member. The first plurality of orifices155 can be configured to deliver a plurality of jet streams 16 ofcoolant 50 into the outlet chamber 150 and against the top surface 12 ofthe thermally conductive base member 430 when pumped coolant 50 isprovided to the inlet chamber 145 of the heat sink module 100, as shownin FIG. 38.

The first plurality of orifices 155 can have an average diameter ofabout 0.001-0.020, 0.001-0.2, 0.001-0.150, 0.001-0.120, 0.001-0.005, or0.030-0.050 in. The first plurality of orifices 155 can have an averagelength of about 0.005-0.25, 0.020-0.1, 0.025-0.08, 0.025-0.075,0.040-0.070, 0.1-0.25, or 0.040-0.070 in. Each orifice 155 of the firstplurality of orifices can have a central axis 17 that is arranged at anangle of about 30-60, 40-50, or 45 degrees with respect to the topsurface 12 of the thermally conductive base member 430. The firstplurality of orifices 155 can be arranged in an array 76 organized intostaggered columns 77 and staggered rows 78, as shown in FIG. 31, suchthat a given orifice 155 in a given column and a given row does not havea corresponding orifice in a neighboring row in the given column or acorresponding orifice in a neighboring column in the given row. Anaverage jet height can be about 0.01-0.75, 0.05-0.5, 0.05-0.25,0.020-0.25, 0.03-0.125, or 0.04-0.08, where the average jet height is anaverage of jet heights 18 measured between the surface 12 of thethermally conductive member 430 and each orifice outlet of each of theplurality of orifices (see, e.g. FIG. 26).

In another example, a heat sink for cooling a heat source can include athermally conductive base member 430 configured to mount on, or beplaced in thermal communication with, a heat source. The heat sink caninclude a heat sink module 100 having a bottom surface 135 configured tomount on a surface 12 of the thermally conductive base member 430. Theheat sink module 100 can include an inlet chamber 145 formed within theheat sink module 100. The heat sink module 100 can include an outletchamber 150 formed at least partially in the heat sink module andbounded by the surface 12 of the thermally conductive base member 430when the heat sink module is mounted on the thermally conductive basemember, as shown in FIG. 26. The heat sink module 100 can include afirst plurality of orifices 155 extending from the inlet chamber 145 tothe outlet chamber 150. The first plurality of orifices 155 can beconfigured to deliver a plurality of jet streams 16 of coolant into theoutlet chamber 150 and against the surface 12 of the thermallyconductive base member 430 when a flow 51 of pumped coolant 50 isprovided to the inlet chamber 145.

The inlet chamber 145 can have a volume of about 0.01-0.02, 0.01-0.05,0.04-0.08, 0.07-0.15, 0.1-0.2, 0.15-0.25, 0.2-0.4, or 0.3-0.5 in³. Theoutlet chamber 150 can have a volume of about 0.02-0.05, 0.04-0.08,0.07-0.15, 0.1-0.2, 0.15-0.25, 0.2-0.4, 0.3-0.5, or 0.4-0.75 in³. Theinlet chamber 145 can decrease in cross-sectional area in a directionaligned with the direction of coolant flow 51, as shown in FIG. 26.Conversely, the outlet chamber 150 can increase in cross-sectional areain a direction aligned with the direction of coolant flow 51, as shownin FIG. 38. The heat sink module 100 can include an inlet passage 165fluidly connecting an inlet port 105 to the inlet chamber 145, as shownin FIG. 26. Likewise, the heat sink module 100 can include an outletpassage 166 fluidly connecting the outlet chamber 150 to an outlet port110, as shown in FIG. 38. The inlet port 105 and outlet port 110 caneach include threads 170 to facilitate connecting sections of flexibletubing 225 to the inlet and outlet ports of the module 100. The inletport 105 can include a central axis 23 defining an angle of about 10-80,20-70, 30-60, or 40-50 degrees with respect to a bottom plane associatedwith the bottom surface 135 of the heat sink module 100, as shown inFIG. 26. The outlet port 110 can include a central axis 24 defining anangle of about 10-80, 20-70, 30-60, or 40-50 degrees with respect to abottom plane associated with the bottom surface 135 of the heat sinkmodule 100, as shown in FIG. 38.

In yet another example, a heat sink can be configured to cool amicroprocessor 415, as shown in FIGS. 28 and 84-89, by transferring heatfrom the microprocessor 415 to a flow 51 of pumped coolant 50 passingthrough the heat sink. The heat sink can include a thermally conductivebase member 430 configured to mount on a surface of a microprocessor415, a heat sink module 100 mounted on a surface 12 of the thermallyconductive base member 430, and a sealing member 125 located between theheat sink module 100 and the surface 12 of the thermally conductive basemember 430. The sealing member 125 can be configured to provide aliquid-tight seal between the heat sink module 430 and the surface 12 ofthe thermally conductive base member 430 to form an outlet chamber 150.The heat sink module 100 can include a plurality of orifices 155configured to deliver a plurality of jet streams 16 of coolant 50 intothe outlet chamber 150 and against the surface 12 of the thermallyconductive base member 430 when pumped coolant is provided to inlets ofthe plurality of orifices 155.

The sealing member 125 can be disposed in a continuous channel 140formed in a bottom surface 135 of the heat sink module 100. Thecontinuous channel 140 can circumscribe the outlet chamber 150. Thesealing member 125 can be at least partially compressed between thecontinuous channel 140 and the surface 12 of the thermally conductivebase member 430 to provide the liquid-tight seal. The heat sink caninclude one or more fasteners 115 securing the heat sink module 100against the surface of the thermally conductive base member 430. The oneor more fasteners 115 can provide a compressive force that compressesthe sealing member 125 between the continuous channel 140 and thesurface 12 of the thermally conductive base member 430.

The heat sink module 100 can include a plurality of anti-poolingorifices 156 arranged in or proximate a rear wall of the outlet chamber150, as shown in FIGS. 24, 34, and 35. The plurality of anti-poolingorifices 156 can have an average diameter of about 0.001-0.020,0.001-0.2, 0.001-0.150, 0.001-0.120, 0.001-0.005, or 0.030-0.050 in. Theplurality of anti-pooling orifices 156 can be configured to deliver aplurality of anti-pooling jet streams 16 of coolant 50 against thesurface of the thermally conductive base member 430 when pumped coolantis provided to inlets of the plurality of anti-pooling orifices 156, asshown in FIG. 38. Each of the plurality of anti-pooling orifices 156 caninclude a central axis 75 (see, e.g. FIG. 35) arranged at an angle ofabout 40-80, 50-70, or 60 degrees with respect to the surface of thethermally conductive base member 430. The heat sink module 100 caninclude one or more boiling-inducing members 196 extending from an innersurface of the outlet chamber 150 toward the surface 12 of the thermallyconductive base member 430, as shown in FIG. 47. A flow clearance 197(see, e.g. FIG. 48) can be provided between ends of the one or moreboiling-inducing members 196 and the surface 12 of the thermallyconductive base member 430. The flow clearance 197 can be about0.001-0.0125, 0.001-0.05, 0.001-0.02, 0.001-0.01, or 0.005-0.010 in.

Examples of Redundant Heat Sink Modules

In one example, a redundant heat sink module 700 can be configured totransfer heat away from a surface to be cooled 12. The redundant heatsink module 700 can include a first independent coolant pathway 701 anda second independent coolant pathway 701. The first independent coolantpathway 701 can be formed within the redundant heat sink module 700 andcan include a first inlet chamber 145-1, a first outlet chamber 150-1,and a first plurality of orifices 155-1 extending from the first inletchamber 145-1 to the first outlet chamber 150-1. The first plurality oforifices 155-1 can be configured to provide a first plurality ofimpinging jet streams 16 of coolant 50 against a first region of asurface to be cooled 12 when the redundant heat sink module 700 ismounted on the surface to be cooled 12 and when pressurized coolant isprovided to the first inlet chamber 145-1. The second independentcoolant pathway 702 can be formed within the redundant heat sink module700 and can include a second inlet chamber 145-2, a second outletchamber 150-2, and a second plurality of orifices 155-2 extending fromthe second inlet chamber 145-2 to the second outlet chamber 150-2. Thesecond plurality of orifices 155-2 can be configured to provide a secondplurality of impinging jet streams 16 of coolant against a second regionof the surface to be cooled 12 when the redundant heat sink module 700is mounted on the surface to be cooled 12 and when pressurized coolantis provided to the second inlet chamber 145-2.

The first plurality of orifices 155-1 can have an average jet height 18of about 0.01-0.75, 0.05-0.5, 0.05-0.25, 0.020-0.25, 0.03-0.125, or0.04-0.08 in. The first plurality of orifices 155-1 can have an averagediameter of D and an average length of L, and L divided by D can begreater than or equal to one or about 1-10, 1-8, 1-6, 1-4, or 1-3. Thefirst plurality of orifices 155-1 have an average diameter of about0.001-0.020, 0.001-0.2, 0.001-0.150, 0.001-0.120, 0.001-0.005,0.020-0.045, 0.030-0.050 in, or 0.040 in.

The first inlet chamber 145-1 can decrease in cross-sectional area in adirection of flow 90, and the first outlet chamber 150-1 can increase incross-sectional area in the direction of flow 90. The second outletchamber 150-2 can circumscribe or be adjacent to the first outletchamber 150-1. The first independent coolant pathway 701 can include ahydrofoil 705 located upstream of the first inlet chamber 145-1. Thehydrofoil 705 can have a curved surface 706 that interacts with the flowof coolant to assist in providing an even distribution of coolant to thefirst plurality of orifices, as shown in FIG. 51N. The redundant heatsink module 700 can include a flow-guiding lip 162 proximate an exit ofthe first outlet chamber, as shown in FIG. 51K. A surface of theflow-guiding lip 162 can have an angle of less than about 45 degreeswith respect to a bottom plane of the redundant heat sink module 700.

In another example, a redundant apparatus for cooling a heat source(e.g. a microprocessor 415) can include a thermally conductive basemember 430, a redundant heat sink module 700 mounted on the thermallyconductive base member 430, and one or more sealing members (125-1,125-2) disposed between the redundant heat sink module 700 and thethermally conductive base member 430. The thermally conductive basemember 430 can be placed in thermal communication with a heat source,such as a microprocessor 415 or a power electronic device. The thermallyconductive base member 430 can include a surface to be cooled 12. Theredundant heat sink module 700 can include a first independent coolantpathway 701 formed within the redundant heat sink module 700. The firstindependent coolant pathway 701 can include a first inlet chamber 145-1,a first outlet chamber 150-1, and a first plurality of orifices 155-1configured to provide a first plurality of impinging jet streams 16 ofcoolant 50 against a first region of the surface to be cooled 12 whenpressurized coolant is provided to the first inlet chamber 145-1. Theredundant heat sink module 700 can include a second independent coolantpathway 702 formed within the redundant heat sink module 700. The secondindependent coolant pathway 702 can include a second inlet chamber145-2, a second outlet chamber 150-2, and a second plurality of orifices155-2 configured to provide a second plurality of impinging jet streams16 of coolant against a second region of the surface to be cooled 12when pressurized coolant is provided to the second outlet chamber 150-2.The one or more sealing members (125-1, 125-5) can be disposed between abottom surface 135 of the redundant heat sink module 700 and a surfaceof the thermally conductive base member 430 to provide a firstliquid-tight seal around a perimeter of the first outlet chamber 150-1and a second liquid-tight seal around a perimeter of the second outletchamber 150-2.

The second region of the surface to be cooled 12 can circumscribe thefirst region of the surface to be cooled 12. The thermally conductivebase member 430 can be a metallic base plate. The thermally conductivebase member 430 can be a heat pipe having a sealed vapor cavity.

In yet another example, a redundant heat sink module 700 for cooling aheat providing surface can include a first independent coolant pathway701 and a second independent coolant pathway 702. The first independentcoolant pathway 701 can include a first inlet chamber 145-1 formedwithin the redundant heat sink module 700 and a first outlet chamber150-1 formed within the redundant heat sink module 700. The first outletchamber 150-1 can have a first open portion configured to be enclosed bythe heat providing surface 12 when the redundant heat sink module 700 issealed against the heat providing surface 12. The first independentcoolant pathway 702 can include a first plurality of orifices 155-1extending from the first inlet chamber 145-1 to the first outlet chamber150-1. The second independent coolant pathway 702 can include a secondinlet chamber 145-2 formed within the redundant heat sink module 700 anda second outlet chamber 150-2 formed within the redundant heat sinkmodule 700. The second outlet chamber 150-2 can have a second openportion configured to be enclosed by the heat providing surface 12 whenthe redundant heat sink module 700 is sealed against the heat providingsurface 12. The second independent coolant pathway 702 can also includea second plurality of orifices 155-2 extending from the second inletchamber 145-2 to the second outlet chamber 150-2.

The first plurality of orifices 155-1 can be arranged at an angle ofabout 20-80, 30-60, 40-50, or 45 degrees with respect to a bottom plane19 of the redundant heat sink module 700. The first plurality oforifices 155-1 can be arranged in an array 76 organized into staggeredcolumns 77 and staggered rows 78 such that a given orifice in a givencolumn and a given row does not have a corresponding orifice in aneighboring row in the given column or a corresponding orifice in aneighboring column in the given row.

The redundant heat sink module 700 can include a plurality ofanti-pooling orifices 156-1 extending from the first inlet chamber 145-1to a rear wall of the first outlet chamber 150-1. The plurality ofanti-pooling orifices 156-1 can be configured to deliver a plurality ofanti-pooling jet streams 16 of coolant 50 to a rear portion of the firstoutlet chamber 150-1 when pressurized coolant 50 is provided to thefirst inlet chamber 145-1. The first inlet chamber 145-1 can have avolume of about 0.01-0.02, 0.01-0.05, 0.04-0.08, 0.07-0.15, 0.1-0.2,0.15-0.25, 0.2-0.4, 0.3-0.5 in³.

The redundant heat sink module 700 can include one or moreboiling-inducing members 196 extending into the first outlet chamber150-1 toward the heat providing surface 12. A flow clearance 197 can beprovided between end portions of the boiling-inducing members 196 and abottom plane 19 of the redundant heat sink module 700, as shown in FIG.48. The flow clearance 197 can be about 0.001-0.0125, 0.001-0.05,0.001-0.02, 0.001-0.01, or 0.005-0.010 in.

The first independent coolant pathway 701 can include an upwardly angledinlet port 105-1 fluidly connected to the first inlet chamber 145-1. Theupwardly angled inlet port 145-1 can have a central axis 24 that definesan angle of about 10-80, 20-70, 30-60, or 40-50 degrees with respect toa bottom plane 19 of the redundant heat sink module 700. The redundantheat sink module 700 can include additional upwardly angled ports(105-2, 110-1, 110-2), as shown in FIG. 51A.

An additive manufacturing process, such as stereolithography, can beused to manufacture the heat sink module 700. The stereolithographyprocess can include forming layers of material curable in response tosynergistic stimulation adjacent to previously formed layers of materialand successively curing the layers of material by exposing the layers ofmaterial to a pattern of synergistic stimulation corresponding tosuccessive cross-sections of the heat sink module. The material curablein response to synergistic stimulation can be a liquid photopolymer.

Examples of Methods

In one example, a method of cooling two heat-providing surfaces (12-1,12-2) within a server 400 using a cooling apparatus 1 having twoseries-connected heat sink modules (100-1, 100-2) can include providinga flow 51 of single-phase liquid coolant 50 to an inlet port 105-1 of afirst heat sink module 100-1 mounted on a first heat-providing surface12-1 within a server 400. A first amount of heat can be transferred fromthe first heat-providing surface 12-1 to the single-phase liquid coolant50 resulting in vaporization of a portion of the single phase liquidcoolant 50 thereby changing the flow 51 of single-phase liquid coolant50 to two-phase bubbly flow containing liquid coolant 50 with vaporcoolant dispersed as bubbles 275 in the liquid coolant 50. The two-phasebubbly flow can have a first quality (x₁). The method can includetransporting the two-phase bubbly flow from an outlet port 110-1 of thefirst heat sink module 100-1 to an inlet port 105-1 of a second heatsink module 100-2. The second heat sink module 100-2 can be mounted on asecond heat-providing surface 12-2 within the server 400. A secondamount of heat can be transferred from the second heat-providing surface12-2 to the two-phase bubbly flow resulting in vaporization of a portionof the liquid coolant 50 within the two-phase bubbly flow therebyresulting in a change from the first quality (x₁) to a second quality(x₂). The second quality can be higher than the first quality (x₂>x₁).The energy from the first amount of heat and the second amount of heatcan be stored, at least in part, as latent heat in the two-phase bubblyflow and transported out of the server 400 through the cooling apparatus1. The amount of heat transferred out of the server 400 can be afunction of the amount of vapor formed within the two-phase bubbly flowand the heat of vaporization of the coolant.

Providing the flow 51 of single-phase liquid coolant 50 to the inletport 105-1 of the first heat sink module 100-1 can include providing aflow rate of about 0.1-10, 0.2-5, 0.25-1.5, 0.3-2.5, 0.6-1.2, or 0.8-1.1liters per minute of single-phase liquid coolant 50 to the first inlet105-1 of the first heat sink module 100-1. The flow 51 of single-phaseliquid coolant 50 can be a dielectric coolant such as, for example,HFE-7000, R-245fa, HFE-7100 or a combination thereof.

Providing the flow 51 of single-phase liquid coolant 50 to the firstheat sink module 100-1 can include providing the flow 51 of single-phaseliquid coolant 50 at a predetermined temperature and a predeterminedpressure, where the predetermined temperature is slightly below thesaturation temperature (T_(sat)) of the single-phase liquid coolant 50at the predetermined pressure. The predetermined temperature can beabout 0.5-20, 0.5-15, 0.5-10, 0.5-7, 0.5-5, 0.5-3, 0.5-1, 1-20, 1-15,1-10, 1-7, 1-5, 1-3, 3-20, 3-15, 3-10, 3-7, 3-5, 5-20, 5-15, 5-10, 5-7,7-20, 7-15, 7-10, 10-20, 10-15, or 15-20 degrees C. below the saturationtemperature of the single-phase liquid coolant 50 at the predeterminedpressure.

A pressure differential of about 0.5-5.0, 0.5-3, or 1-3 psi can bemaintained between the inlet port 105-1 of the first heat sink module100-1 and the outlet port 110-1 of the first heat sink module 100-1. Thepressure differential can be suitable to promote the flow 51 to advancefrom the inlet port 105-1 of the first heat sink module 100-1 to theoutlet port 110-1 of the first heat sink module 100-1.

A saturation temperature (T_(sat), x₂) and pressure of the two-phasebubbly flow having a second quality (x₂) can be less than a saturationtemperature (T_(sat), x₁) and pressure of the two-phase flow having afirst quality (x₁) (as shown in FIG. 14B), thereby allowing the secondheat-providing surface 12-2 to be maintained at a lower temperature thanthe first heat-providing surface 12-1 when a first heat flux from thefirst heat-providing surface is approximately equal to a second heatflux from the second heat-providing surface.

The first quality (x₁) can be about 0-0.1, 0.05-0.15, 0.1-0.2,0.15-0.25, 0.2-0.3, 0.25-0.35, 0.3-0.4, 0.35-0.45, 0.4-0.5, 0.45-0.55,and the second quality (x₂) can be greater than the first quality, suchas, for example, 0-0.1, 0.05-0.15, 0.1-0.2, 0.15-0.25, 0.2-0.3,0.25-0.35, 0.3-0.4, or 0.4-0.45 greater than the first quality.

The liquid component 50 of the two-phase bubbly flow that is transportedbetween the first heat sink module 100-1 and the second heat sink module100-2 can have a temperature slightly below its saturation temperature.The pressure of the two-phase bubbly flow can be about 0.5-5.0, 0.5-3,or 1-3 psi less than the predetermined pressure of the flow 51 ofsingle-phase liquid coolant 50 provided to the inlet port 105-1 of thefirst heat sink module 100-1.

The first heat-providing surface 12-1 can be a surface of amicroprocessor 415 within the server 400. The first heat-providingsurface 12-1 can be a surface of a thermally conductive base member 430in thermal communication with a microprocessor 415 within the server400. The thermally conductive base member 430 can be a metallic baseplate mounted on the microprocessor 415 using a thermal interfacematerial.

In another example, a method of cooling two or more heat-providingsurfaces (12-1, 12-2) using a cooling apparatus 1 having two or morefluidly connected heat sink modules (e.g. 100-1, 100-2) arranged in aseries configuration can include providing a flow 51 of single-phaseliquid coolant 50 to a first inlet port 105-1 of a first heat sinkmodule 100-1 mounted on a first surface to be cooled 12-1. The flow 51of single-phase liquid coolant 50 can have a predetermined pressure anda predetermined temperature at the first inlet port 105-1 of the firstheat sink module 100-1. The predetermined temperature can be slightlybelow a saturation temperature of the coolant at the predeterminedpressure. The method can include projecting the flow 51 of single-phaseliquid coolant 50 against the first heat-providing surface 12-1 withinthe first heat sink module 100-1, where a first amount of heat istransferred from the first heat-providing surface 12-1 to the flow 51 ofsingle-phase liquid coolant 50 thereby inducing phase change in aportion of the single-phase liquid coolant 50 and thereby changing theflow 51 of single-phase liquid coolant to two-phase bubbly flowcontaining a liquid coolant 50 and a plurality of vapor bubbles 275dispersed within the liquid coolant 50. The plurality of vapor bubbles275 can have a first number density.

The method can include providing a second heat sink module 100-2 mountedon a second heat-providing surface 12-2. The second heat sink module100-2 can include a second inlet port 105-2 and a second outlet port110-2. The method can include providing a first section of tubing 225having a first end connected to the first outlet port 110-1 of the firstheat sink module 100-1 and a second end connected to the second inletport 105-2 of the second heat sink module 100-2. The first section oftubing 225 can transport the two-phase bubbly flow having the firstnumber density of vapor bubbles from the first outlet port 110-1 of thefirst heat sink module 100-1 to the second inlet port 105-2 of thesecond heat sink module 100-2. The method can include projecting thetwo-phase bubbly flow having the first number density against the secondheat-providing surface 12-2 within the second heat sink module 100-2,where a second amount of heat is transferred from the secondheat-providing surface 12-2 to the two-phase bubbly flow having a firstnumber density and thereby changing two-phase bubbly flow having a firstnumber density to a two-phase bubbly flow having a second number densitygreater than the first number density.

A saturation temperature and pressure of the two-phase flow having asecond number density can be less than a saturation temperature andpressure of the two-phase flow having a first number density, therebyallowing the second heat-providing surface 12-2 to be maintained at alower temperature than the first heat-providing surface 12-1 when afirst heat flux from the first heat-providing surface is approximatelyequal to a second heat flux from the second heat-providing surface.

The predetermined temperature of the flow 51 of single-phase liquidcoolant 50 at the first inlet port 105-1 of the first heat sink module100-1 can be about 0.5-20, 0.5-15, 0.5-10, 0.5-7, 0.5-5, 0.5-3, 0.5-1,1-20, 1-15, 1-10, 1-7, 1-5, 1-3, 3-20, 3-15, 3-10, 3-7, 3-5, 5-20, 5-15,5-10, 5-7, 7-20, 7-15, 7-10, 10-20, 10-15, or 15-20 degrees C. below thesaturation temperature of the flow 51 of single-phase liquid coolant 50at the predetermined pressure of the flow 51 of single-phase liquidcoolant at the first inlet of the first heat sink module.

Providing the flow 51 of single-phase liquid coolant 50 to the inletport 105-1 of the first heat sink module 100-1 can include providing aflow rate of about 0.1-10, 0.2-5, 0.3-2.5, 0.6-1.2, or 0.8-1.1 litersper minute of single-phase liquid coolant 50 to the first inlet port100-1 of the first heat sink module 100-1.

The liquid in the two-phase bubbly flow being transported between thefirst heat sink module 100-1 and the second heat sink module 100-2 canhave a temperature at or slightly below its saturation temperature,where a pressure of the two-phase bubbly flow having a first numberdensity is about 0.5-5.0, 0.5-3, or 1-3 psi less than the predeterminedpressure of the flow 51 of single-phase liquid coolant 50 provided tothe first heat sink module 100-1.

The first heat sink module 100-1 can include an inlet chamber 145 formedwithin the first heat sink module and an outlet chamber 150 formedwithin the first heat sink module. The outlet chamber 150 can have anopen portion enclosed by the first surface to be cooled 12-1 when thefirst heat sink module 100-1 is mounted on the first surface to becooled 12-1. The first heat sink module 100-1 can include a plurality oforifices 155 extending from the inlet chamber 145 to the outlet chamber150. Projecting the flow 51 of single-phase liquid coolant 50 againstthe first heat-providing surface 12-1 can include projecting a pluralityof jet streams 16 of single-phase liquid coolant 50 through theplurality of orifices 155 into the outlet chamber 150 and against thefirst surface to be cooled 12-1 when the flow 51 of single-phase liquidcoolant 50 is provided to the inlet chamber 145 from the first inletport 105-1 of the first heat sink module 100-1. The first plurality oforifices 155 can have an average diameter of about 0.001-0.020,0.001-0.2, 0.001-0.150, 0.001-0.120, 0.001-0.005, or 0.030-0.050 inches.Outlets of the plurality of orifices 155 can be arranged at a jet height18 from the first surface to be cooled 12-1. The jet height 18 can beabout 0.01-0.75, 0.05-0.5, 0.05-0.25, 0.020-0.25, 0.03-0.125, or0.04-0.08 inches. At least one of the orifices 155 can have a centralaxis 74 arranged at an angle of about 30-60, 40-50, or 45 degrees withrespect to the first surface to be cooled 12-1.

In another example, a method of cooling two microprocessors 415 on amotherboard 405 using a two-phase cooling apparatus 1 having twoseries-connected heat sink modules (100-1, 100-2) can include providinga flow 51 of single-phase liquid coolant 50 to an inlet port 105 of afirst heat sink module 100-1 mounted on a first thermally conductivebase member 430. The first thermally conductive base member 430 can bemounted on a first microprocessor 415 mounted on a motherboard 405,where heat is transferred from the first microprocessor 415 through thefirst thermally conductive base member 430 and to the flow 51 ofsingle-phase liquid coolant 50 resulting in boiling of a first portionof the single-phase liquid coolant 50, thereby changing the flow 51 ofsingle-phase liquid coolant 50 to two-phase bubbly flow having a firstquality (x₁). The method can include transporting the two-phase bubblyflow from an outlet port 110 of the first heat sink module 100-1 to aninlet port 105 of a second heat sink module 100-2 through flexibletubing 225. The second heat sink module 100-2 can be mounted on a secondthermally conductive base member 430 that is mounted on a secondmicroprocessor 415 mounted on the motherboard 405. Heat can betransferred from the second microprocessor 415 through the secondthermally conductive base member 430 and to the two-phase bubbly flowresulting in vaporization of a portion of liquid coolant 50 within thetwo-phase bubbly flow thereby resulting in a change from the firstquality (x₁) to a second quality (x₁), the second quality being higherthan the first quality (i.e. x₂>x₁).

Examples of Cooling Apparatuses

In one example, a flexible two-phase cooling apparatus 1 for coolingmicroprocessors 415 in servers 400 can include a primary cooling loop300, a first bypass 305, and a second bypass 310. The primary coolingloop 300 can be configured to circulate a dielectric coolant 50. Theprimary cooling loop 300 can include a reservoir 200, a pump 20downstream of the reservoir 200, an inlet manifold 210 downstream of thepump 20, an outlet manifold 215 downstream of the inlet manifold 210,and two or more flexible cooling lines 303 extending from the inletmanifold 210 to the outlet manifold 215, as shown in FIG. 79. The two ormore flexible cooling lines 303 can each be routable within a serverhousing 400, as shown in FIG. 84, and can each be fluidly connected totwo or more series-connected heat sink modules. The two or more flexiblecooling lines can be configured to transport low-pressure, two-phasedielectric coolant 50. Each heat sink module 100 can include a thermallyconductive base member 430 sized to cover a top surface of amicroprocessor 415, as shown in FIG. 28. A thermal interface material435 can be provided between the thermally conductive base member 430 andthe microprocessor 415. The cooling apparatus 1 can include a firstbypass 305 having a first end and a second end. The first end of thefirst bypass 305 being can be connected to the primary cooling loop 300downstream of the pump 20 and upstream of the inlet manifold 210, asshown in FIG. 79. The second end of the first bypass 305 can beconnected at or upstream of the reservoir 200. The first bypass 305 caninclude a first pressure regulator 60-1 configured to regulate a firstbypass flow 51-1 of coolant through the first bypass 305. The coolingapparatus 1 can include a second bypass 310 having a first end and asecond end. The first end of the second bypass 310 can be connected tothe inlet manifold 210, and the second end of the second bypass 310 canbe connected to the outlet manifold 215, as shown in FIG. 79. The secondbypass 310 can include a second pressure regulator 60-2 configured toregulate a second bypass flow 51-3 of coolant through the second bypass310.

Each of the two or more flexible cooling lines 303 can have a minimumbend radius R of less than 3, 2.5, or 2 inches to permit routing withina server housing 400, as shown in FIG. 84. Each of the two or moreflexible cooling lines 303 can have an inner diameter of about0.125-0.250 or 0.165-0.185 inches and an outer diameter of about 0.2-0.4inches. The primary cooling loop 300 can be configured to circulate adielectric coolant 50 having a boiling point of about 15-35, 20-45,30-55, or 40-65 degrees C. determined at a pressure of 1 atm. Each ofthe two or more flexible cooling lines 303 can be low pressure coolinglines with a maximum operating pressure of less than 50, 75, or 100 psi.The first bypass 305 can include a heat exchanger 40-1 downstream of thefirst pressure regulator 60-1, as shown in FIG. 79. The heat exchanger40-1 can be a liquid-to-liquid heat exchanger configured to fluidlyconnect to an external heat rejection loop 43.

The first pressure regulator 60-1 can be configured to provide apressure differential of about 5-20 psi between an inlet and an outletof the first pressure regulator 60-1. Likewise, the second pressureregulator 60-2 can be configured to provide a pressure differential ofabout 5-20 psi between an inlet and an outlet of the second pressureregulator 60-2. The cooling apparatus 1 can be configured to hold apredetermined amount of coolant 50. The reservoir 200 can have an innervolume configured to hold at least 15% of the predetermined amount ofcoolant in the cooling apparatus 1.

In another example, a flexible two-phase cooling apparatus 1 for coolingone or more heat-generating devices can include a primary cooling loop300, a first bypass 305, and a second bypass 310, as shown in FIG. 81.The primary cooling loop 300 can include a pump 20 configured to providea flow 51 of pressurized liquid coolant though the primary cooling loop300. The primary cooling loop 300 can include a heat sink module 100fluidly connected to the primary cooling loop 300. The heat sink module100 can be configured to mount on and remove heat from a surface 12 of aheat-generating device. The primary cooling loop can include a reservoir200 fluidly connected to the primary cooling loop 300 upstream of thepump 20. The first bypass 305 can have a first end and a second end. Thefirst end of the first bypass 305 can be fluidly connected to theprimary cooling loop 300 downstream of the pump 20. The second end ofthe first bypass 305 can be fluidly connected to the primary coolingloop 300 upstream of the pump 20. The first bypass can include a firstheat exchanger 40-1 and a first pressure regulator 60-1. The firstpressure regulator 60-1 can be configured to adjust a first bypass flow51-1 through the first heat exchanger 40-1. The first heat exchanger40-1 can be configured to subcool the first bypass flow 51-1 ofpressurized coolant below a saturation temperature (T_(sat)) of thepressurized coolant. A second bypass 310 can have a first end and asecond end. The first end of the second bypass 310 can be fluidlyconnected to the primary cooling loop 300 downstream of the pump andupstream of the one or more heat sink modules 100. The second end of thesecond bypass 310 can be fluidly connected to the primary cooling loop300 downstream of the one or more heat sink modules 100 and upstream ofthe reservoir 200. The second bypass 310 can include a second pressureregulator 60-2 configured to adjust a second bypass flow 51-3 ofpressurized coolant through the second bypass 310.

The pump 20 can be configured to provide the flow of pressurized coolantat a pressure of about 5-20, 15-25, 20-35, or 25-45 psia, where thepressure is measured at the pump outlet 22. At least a portion of theprimary cooling loop 300 can include a section of flexible tubing 225fluidly connected to the heat sink module 100. The section of flexibletubing 225 can have a minimum bend radius of less than about 3, 2.5, or2 inches. The section of flexible tubing 225 can have a maximumoperating pressure of less than 50, 75, or 100 psi.

The heat sink module 100 can include an inlet chamber 145, an outletchamber 150, and a dividing member 195, as shown in FIG. 26. The inletchamber 145 can be formed within the heat sink module 100. The outletchamber 150 can be formed within the heat sink module 100. The outletchamber 150 can have an open portion along a bottom surface 135 of theheat sink module 100. The open portion 152 (see, e.g. FIG. 25) can beenclosed by and sealed against a thermally conductive base member 430,as shown in FIG. 26. A sealing member 125 can be provided between theheat sink module 100 and the thermally conductive base member 430 tofacilitate sealing. The thermally conductive base member 430 can beconfigured to mount on a heat-generating device (e.g. a microprocessor415), as shown in FIG. 28, using a thermal interface material 435. Thedividing member 195 can be disposed between the inlet chamber 145 andthe outlet chamber 150. The dividing member 195 can include a firstplurality of orifices 155 formed in the dividing member 195. The firstplurality of orifices 155 can extend from a top surface of the dividingmember 195 to a bottom surface of the dividing member 195. The firstplurality of orifices 155 can be configured to deliver a plurality ofjet streams 16 of coolant 50 into the outlet chamber 150 and against asurface of the thermally conductive base member 430 when the heat sinkmodule 100 is installed on the heat-generating device and whenpressurized coolant is provided to the inlet chamber 145, as shown inFIG. 26. The first plurality of orifices 155 can have an averagediameter of about 0.001-0.020, 0.001-0.2, 0.001-0.150, 0.001-0.120,0.001-0.005, or 0.030-0.050 in. The first plurality of orifices 155 canhave an average diameter of D and an average length of L, and L dividedby D can be greater than or equal to one or about 1-10, 1-8, 1-6, 1-4,or 1-3.

In yet another example, a flexible two-phase cooling apparatus 1 forcooling a microprocessor 415 can include a primary cooling loop 300 anda bypass 310, as shown in FIG. 82. The primary cooling loop 300 caninclude a pump 200 configured to provide a flow 51 of pressurizedcoolant through the primary cooling loop 300. The primary cooling loop300 can include a first heat sink module 100 fluidly sealed against athermally conductive base member 430. The heat sink module 100 can beconfigured to mount on a surface of a microprocessor 415 such that thethermally conductive base member 430 is in thermal communication withthe microprocessor 415. The first heat sink module 100 can include aplurality of internal orifices 155 that are configured to transform atleast a portion of the flow 51 of pressurized coolant into a pluralityof jet streams 16 of coolant 50 directed at a surface of the thermallyconductive base member 430, as shown in FIG. 26. The plurality of jetstreams 16 of coolant 50 can be configured to remove heat from thethermally conductive base member 430 by way of latent heat transfer as afraction of the coolant from the plurality of jet streams 16 changesphase to vapor bubbles 275 as a result of absorbing heat from thethermally conductive base member 430, the heat originating from themicroprocessor 415. The bypass 310 can have a first end and a secondend. The first end of the bypass 310 can be fluidly connected to theprimary cooling loop 300 upstream of the heat sink module 100. Thesecond end of the bypass 310 can be fluidly connected to the primarycooling loop 300 downstream of the heat sink module 100. The bypass 310can include a pressure regulator 60-2 configured to allow a pressuredifferential to be established between an inlet 105 of the heat sinkmodule 100 and an outlet 110 of the heat sink module 100 to control aflow rate ({dot over (V)}_(line)) of pressurized coolant through theheat sink module. The pressure regulator 60-2 can be configured to allowa pressure differential of about 0.5-3, 1-5, 5-25, 5-20, 10-15, or about12 psi to be established between an inlet 105 of the heat sink moduleand an outlet 110 of the heat sink module.

The primary cooling loop 300 can include a second heat sink module 100fluidly connected in series with the first heat sink module, as shown inFIG. 84. The outlet port 110 of the first heat sink module 100 can befluidly connected to an inlet port 105 of the second heat sink module100 by a section of flexible tubing 225 having a minimum bend radius ofless than about 3, 2.5, or 2 inches. The section of flexible tubing 225can be low-pressure tubing having a maximum operating pressure of lessthan 50, 75, or 100 psi. The flow rate ({dot over (V)}_(line)) ofpressurized coolant through the first and second series-connected heatsink modules 100 can be about 0.25-5, 0.5-3, 0.5-2, or 0.8-1.2 litersper minute.

The cooling apparatus 1 can include a second bypass 305 having a firstend and a second end, as shown in FIG. 82. The first end of the secondbypass 305 can be fluidly connected to the primary cooling loop 300downstream of the pump and upstream of the heat sink module 100. Thesecond end of the second bypass 305 can be fluidly connected to theprimary cooling loop 300 downstream of the one or more heat sink modules100 and upstream of a reservoir 200. The second bypass 305 can include asecond pressure regulator 60-1 configured to adjust a second bypass flow51-1 of pressurized coolant through the second bypass. The second bypasscan include a heat exchanger configured to provide subcooling of thesecond bypass flow 51-1 of pressurized coolant.

The coolant 50 can be a dielectric coolant with a boiling point of about15-35, 20-45, 30-55, or 40-70 degrees C. determined at a pressure of 1atm. The dielectric coolant 50 can be homogeneous or, in some examples,can be a mixture of R-245fa and HFE 7000, such as about 5-50, 10-35, or15-25% R-245fa by volume.

The elements and method steps described herein can be used in anycombination whether explicitly described or not. All combinations ofmethod steps as described herein can be performed in any order, unlessotherwise specified or clearly implied to the contrary by the context inwhich the referenced combination is made.

As used herein, the singular forms “a,” “an,” and “the” include pluralreferents unless the content clearly dictates otherwise.

Numerical ranges as used herein are intended to include every number andsubset of numbers contained within that range, whether specificallydisclosed or not. Further, these numerical ranges should be construed asproviding support for a claim directed to any number or subset ofnumbers in that range. For example, a disclosure of from 1 to 10 shouldbe construed as supporting a range of from 2 to 8, from 3 to 7, from 5to 6, from 1 to 9, from 3.6 to 4.6, from 3.5 to 9.9, and so forth.

All patents, patent publications, and peer-reviewed publications (i.e.,“references”) cited herein are expressly incorporated by reference tothe same extent as if each individual reference were specifically andindividually indicated as being incorporated by reference. In case ofconflict between the present disclosure and the incorporated references,the present disclosure controls.

The methods and compositions of the present invention can comprise,consist of, or consist essentially of the essential elements andlimitations described herein, as well as any additional or optionalsteps, components, or limitations described herein or otherwise usefulin the art.

It is understood that the invention is not confined to the particularconstruction and arrangement of parts herein illustrated and described,but embraces such modified forms thereof as come within the scope of theclaims.

Several impingement technologies exist, but few have shown commercialpromise and none have gained wide-scale commercial acceptance to datedue to instability issues, relatively high flow rate requirements,limitations on scalability, and other shortcomings.

Improved heat sink modules (100, 700) with one or more arrays 96 ofimpinging jet streams 16 have been developed and are described herein.The heat sink modules can be connected in series and/or parallelconfigurations to cool a plurality of heat sources 12 simultaneously,thereby providing a scalable jet impingement technology. Importantly,the heat sink modules described herein are compact and easy to packagewithin new and existing server and personal computer housings. The heatsink modules can also be easily packaged in a wide variety of otherelectrical and mechanical devices that require a highly efficient andscalable cooling apparatus 1.

The foregoing description has been presented for purposes ofillustration and description. It is not intended to be exhaustive or tolimit the claims to the embodiments disclosed. Other modifications andvariations may be possible in view of the above teachings. Theembodiments were chosen and described to explain the principles of theinvention and its practical application to enable others skilled in theart to best utilize the invention in various embodiments and variousmodifications as are suited to the particular use contemplated. It isintended that the claims be construed to include other alternativeembodiments of the invention except insofar as limited by the prior art.

What is claimed is:
 1. A method of cooling two or more processors of aserver by absorbing sensible heat and latent heat in coolant flowingthrough two or more series-connected heat sink modules, the methodcomprising: providing a flow of subcooled single-phase liquid coolant toan inlet of a first heat sink module in thermal communication with afirst processor of a server, wherein the subcooled single-phase liquidcoolant absorbs a first amount of heat from the first processor assensible heat; and transporting the flow of subcooled single-phaseliquid coolant from an outlet of the first heat sink module to an inletof a second heat sink module in thermal communication with a secondprocessor of the server, wherein the flow of subcooled single-phaseliquid absorbs a second amount of heat from the second processor assensible heat resulting in the flow of subcooled single-phase liquidcoolant reaching its saturation temperature and becoming a flow ofsaturated single-phase liquid coolant, wherein the flow of saturatedsingle-phase liquid coolant absorbs a third amount of heat from thesecond processor as latent heat resulting in vaporization of a firstportion of the flow of saturated single-phase liquid coolant therebychanging the flow of saturated single-phase liquid coolant to two-phasebubbly flow comprising saturated liquid coolant with vapor coolantdispersed as bubbles in the saturated liquid coolant.
 2. The method ofclaim 1, further comprising: transporting the flow of two-phase bubblyflow comprising the first amount of heat, the second amount of heat, andthe third amount of heat out of the server through a flexible coolingline; and rejecting the first amount of heat, the second amount of heat,and the third amount of heat from the flow of two-phase bubbly flow bydirecting the flow of two-phase bubbly flow through a heat exchangerfluidly connected to a heat rejection loop.
 3. The method of claim 1,further comprising projecting the flow of subcooled single-phase liquidcoolant, in the form of impinging jet streams, against a first surfaceto be cooled within the first heat sink module.
 4. The method of claim1, further comprising projecting the flow of subcooled single-phaseliquid coolant, in the form of impinging jet streams, against a secondsurface to be cooled within the second heat sink module.
 5. The methodof claim 1, wherein providing the flow of subcooled single-phase liquidcoolant to the inlet of the first heat sink module comprises providing aflow rate of about 0.1-10, 0.2-5, 0.3-2.5, 0.6-1.2, or 0.8-1.1 litersper minute of subcooled single-phase liquid coolant to the first inletof the first heat sink module.
 6. The method of claim 1, whereinproviding the flow of subcooled single-phase liquid coolant to the inletof the first heat sink module comprises providing a subcooledsingle-phase liquid coolant with a boiling point of about 15-35, 20-45,30-55, or 40-65 degrees C. determined at a pressure of 1 atm.
 7. Themethod of claim 1, wherein providing the flow of subcooled single-phaseliquid coolant to the inlet of the first heat sink module comprisesproviding a dielectric coolant comprising a hydrofluoroether, ahydrofluorocarbon, or a combination thereof.
 8. The method of claim 1,wherein providing the flow of subcooled single-phase liquid coolant tothe first heat sink module comprises providing a flow of subcooledsingle-phase liquid coolant at a predetermined temperature and apredetermined pressure, wherein the predetermined temperature is belowthe saturation temperature of the flow of subcooled single-phase liquidcoolant at the predetermined pressure.
 9. The method of claim 8, whereinthe predetermined temperature is about 0.5-20, 0.5-15, 0.5-10, 0.5-7,0.5-5, 0.5-3, 0.5-1, 1-20, 1-15, 1-10, 1-7, 1-5, 1-3, 3-20, 3-15, 3-10,3-7, 3-5, 5-20, 5-15, 5-10, 5-7, 7-20, 7-15, 7-10, 10-20, 10-15, or15-20 degrees C. below the saturation temperature of the flow ofsubcooled single-phase liquid coolant at the predetermined pressure. 10.The method of claim 1, further comprising providing a pressuredifferential of about 0.5-5.0, 0.5-3, or 1-3 psi between the inlet ofthe first heat sink module and the outlet of the first heat sink module,wherein the pressure differential is suitable to promote the flow toadvance from the inlet of the first heat sink module to the outlet ofthe first heat sink module.
 11. The method of claim 1, furthercomprising transporting the two-phase bubbly flow having a first qualityfrom an outlet of the second heat sink module to an inlet of a thirdheat sink module connected in series with the first and second heat sinkmodules, wherein the third heat sink module is in thermal communicationwith a third processor of the server, wherein the two-phase bubbly flowhaving the first quality absorbs a fourth amount of heat from the thirdprocessor as latent heat resulting in vaporization of a second portionof the saturated single-phase liquid coolant thereby changing the flowfrom two-phase bubbly flow with the first quality to two-phase bubblyflow with a second quality greater than the first quality.
 12. Themethod of claim 1, further comprising directing the flow of subcooledsingle-phase liquid coolant through one or more series-connected heatsink modules prior to providing the flow of subcooled single-phaseliquid coolant to the inlet of the first heat sink module.
 13. A methodof absorbing heat from two or more processors in an electronic device byflowing coolant through two or more fluidly connected heat sink modulesarranged in a series configuration, the method comprising: providing aflow of subcooled single-phase liquid coolant to a first heat sinkmodule, the first heat sink module comprising a first thermallyconductive base member in thermal communication with a first processorin an electronic device, the flow of subcooled single-phase liquidcoolant having a predetermined pressure and a predetermined temperatureat a first inlet of the first heat sink module, the predeterminedtemperature being below a saturation temperature of the flow ofsubcooled single-phase liquid coolant at the predetermined pressure;projecting the flow of subcooled single-phase liquid coolant against thethermally conductive base member within the first heat sink module,wherein the flow of subcooled single-phase liquid coolant absorbs afirst amount of heat from the first processor through the thermallyconductive base member as sensible heat; providing a second heat sinkmodule comprising a second thermally conductive base member in thermalcommunication with a second processor, the second heat sink modulecomprising a second inlet; providing a first section of tubing having afirst end connected to the first outlet of the first heat sink moduleand a second end connected to the second inlet of the second heat sinkmodule; transporting through the first section of tubing the flow ofsubcooled single-phase liquid coolant from the first outlet of the firstheat sink module to the second inlet of the second heat sink module; andprojecting the flow of subcooled single-phase liquid coolant against thesecond thermally conductive base member within the second heat sinkmodule, wherein the flow of subcooled single-phase liquid coolantabsorbs a second amount of heat from the second processor through thesecond thermally conductive base member as sensible heat resulting inthe flow of subcooled single-phase liquid coolant reaching itssaturation temperature and becoming a flow of saturated single-phaseliquid coolant, wherein the flow of saturated single-phase liquidcoolant absorbs a third amount of heat from the second processor throughthe second thermally conductive base member as latent heat resulting invaporization of a first portion of the flow of saturated single-phaseliquid coolant thereby changing the flow of saturated single-phaseliquid coolant to two-phase bubbly flow comprising saturated liquidcoolant with vapor coolant dispersed as bubbles in the saturated liquidcoolant.
 14. The method of claim 13, further comprising transporting theflow of two-phase bubbly flow comprising the first amount of heat, thesecond amount of heat, and the third amount of heat out of theelectronic device through a flexible cooling line.
 15. The method ofclaim 13, wherein projecting the flow of subcooled single-phase liquidcoolant against the thermally conductive base member within the firstheat sink module comprising projecting a plurality of jet streams ofsubcooled single-phase liquid against the thermally conductive basemember within the first heat sink module.
 16. The method of claim 13,further comprising directing the flow of subcooled single-phase liquidcoolant through one or more series-connected heat sink modules prior toproviding the flow of subcooled single-phase liquid coolant to the inletof the first heat sink module.
 17. The method of claim 13, whereinproviding a first section of tubing comprises providing a section offlexible tubing having a minimum bend radius of less than 3, 2.5, or 2inches to permit routing within the electronic device.
 18. The method ofclaim 13, wherein the electronic device is a server, a personalcomputer, a tablet computer, a power electronics device, a smartphone,an automotive electronic control unit, a battery management device, aprogressive gaming device, a telecommunications system, a highperformance computing system, a server-based gaming device, an avionicssystem, or a home automation control unit.
 19. The method of claim 13,wherein the first processor is a central processing unit (CPU) or agraphics processing unit (GPU), and wherein the second processor is aCPU or a GPU.
 20. A method of absorbing heat from two or more devicesusing a two-phase cooling apparatus configured to pump low-pressurecoolant through two or more fluidly-connected and series-connected heatsink modules, the method comprising: providing a flow of subcooledsingle-phase liquid coolant to an inlet of a first heat sink module inthermal communication with a first device, wherein the flow of subcooledsingle-phase liquid coolant absorbs a first amount of heat from thefirst device as sensible heat within the first heat sink module;transporting the flow of subcooled single-phase liquid coolant from anoutlet of the first heat sink module to an inlet of a second heat sinkmodule, wherein the flow of subcooled single-phase liquid coolantabsorbs a second amount of heat from the second device partially assensible heat and partially as latent heat and becomes two-phase bubblyflow comprising saturated liquid coolant with vapor bubbles of coolantdispersed in the saturated liquid coolant; and transporting thetwo-phase bubbly flow comprising the first amount of heat and the secondamount of heat away from the first and second devices.